diff --git a/src/__tests__/round-trip-unrecognized-extras.test.ts b/src/__tests__/round-trip-unrecognized-extras.test.ts
new file mode 100644
index 0000000..0cff877
--- /dev/null
+++ b/src/__tests__/round-trip-unrecognized-extras.test.ts
@@ -0,0 +1,188 @@
+/**
+ * Round-trip tests for the `.chart`/`.mid` preservation buckets that landed
+ * after the writer stack was authored:
+ *
+ *   - `metadata.extraChartSongFields`   — unknown `[Song]` keys (.chart)
+ *   - `unrecognizedSyncTrackEvents`     — non-B/TS `[SyncTrack]` lines (.chart)
+ *   - `unrecognizedEventsTrackMidiEvents` — non-text MIDI events on the EVENTS
+ *                                            track (e.g. RB practice-assist
+ *                                            notes 24/25/26)
+ *
+ * All tests go through `parseChartAndIni` on the writer output and assert on
+ * the resulting `ParsedChart` — no assertions about the raw serialized bytes.
+ */
+
+import { describe, expect, it } from 'vitest'
+
+import { createEmptyChart } from '../chart/create-chart'
+import { writeChartFile } from '../chart/chart-writer'
+import { writeMidiFile } from '../chart/midi-writer'
+import { parseChartAndIni, type ParsedChart } from '../chart/parse-chart-and-ini'
+
+function roundTripChart(chart: ParsedChart): ParsedChart {
+	const bytes = new TextEncoder().encode(writeChartFile(chart))
+	const result = parseChartAndIni([{ fileName: 'notes.chart', data: bytes }])
+	if (!result.parsedChart) {
+		throw new Error(`round-trip produced no parsedChart: ${JSON.stringify(result.chartFolderIssues)}`)
+	}
+	return result.parsedChart
+}
+
+function roundTripMidi(chart: ParsedChart): ParsedChart {
+	const bytes = writeMidiFile(chart)
+	const result = parseChartAndIni([{ fileName: 'notes.mid', data: bytes }])
+	if (!result.parsedChart) {
+		throw new Error(`round-trip produced no parsedChart: ${JSON.stringify(result.chartFolderIssues)}`)
+	}
+	return result.parsedChart
+}
+
+// ---------------------------------------------------------------------------
+// metadata.extraChartSongFields
+// ---------------------------------------------------------------------------
+
+describe('writeChartFile round-trip: metadata.extraChartSongFields', () => {
+	it('preserves Moonscraper / GHTCP legacy fields verbatim', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = {
+			Player2: 'bass',
+			PreviewEnd: '0',
+			MediaType: 'cd',
+			MusicStream: 'song.ogg',
+			GuitarStream: 'guitar.ogg',
+			HoPo: '0',
+		}
+		const re = roundTripChart(chart)
+		expect(re.metadata.extraChartSongFields).toEqual({
+			Player2: 'bass',
+			PreviewEnd: '0',
+			MediaType: 'cd',
+			MusicStream: 'song.ogg',
+			GuitarStream: 'guitar.ogg',
+			HoPo: '0',
+		})
+	})
+
+	it('preserves quoted string values including inner spaces', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = {
+			ArtistText: '"by"',
+			MusicStream: '"Some Song.ogg"',
+		}
+		const re = roundTripChart(chart)
+		expect(re.metadata.extraChartSongFields).toEqual({
+			// The parser strips one layer of enclosing quotes on read. What matters
+			// is that the key survives and the value round-trips: re-writing the
+			// stripped form re-adds no quotes, so the next parse sees it unquoted.
+			ArtistText: 'by',
+			MusicStream: 'Some Song.ogg',
+		})
+	})
+
+	it('preserves future / unknown keys the parser has never heard of', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = { FutureField: 'future-value', Boss: '1' }
+		expect(roundTripChart(chart).metadata.extraChartSongFields).toEqual({
+			FutureField: 'future-value',
+			Boss: '1',
+		})
+	})
+
+	it('is still undefined when no extras are set', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		expect(roundTripChart(chart).metadata.extraChartSongFields).toBeUndefined()
+	})
+})
+
+// ---------------------------------------------------------------------------
+// unrecognizedSyncTrackEvents
+// ---------------------------------------------------------------------------
+
+describe('writeChartFile round-trip: unrecognizedSyncTrackEvents', () => {
+	it('preserves tempo anchors (A) verbatim', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.unrecognizedSyncTrackEvents.push(
+			{ tick: 0, text: 'A 0' },
+			{ tick: 3840, text: 'A 8805460' },
+		)
+		expect(roundTripChart(chart).unrecognizedSyncTrackEvents).toEqual([
+			{ tick: 0, text: 'A 0' },
+			{ tick: 3840, text: 'A 8805460' },
+		])
+	})
+
+	it('preserves unknown / future SyncTrack event types verbatim', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.unrecognizedSyncTrackEvents.push({ tick: 1920, text: 'FUTURE 12 34 56' })
+		expect(roundTripChart(chart).unrecognizedSyncTrackEvents).toEqual([
+			{ tick: 1920, text: 'FUTURE 12 34 56' },
+		])
+	})
+
+	it('does not disturb tempos or time signatures at the same tick', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.tempos.push({ tick: 960, beatsPerMinute: 150, msTime: 0 })
+		chart.timeSignatures.push({ tick: 960, numerator: 3, denominator: 4, msTime: 0, msLength: 0 })
+		chart.unrecognizedSyncTrackEvents.push({ tick: 960, text: 'A 12345' })
+		const re = roundTripChart(chart)
+		expect(re.tempos.find(t => t.tick === 960)?.beatsPerMinute).toBe(150)
+		expect(re.timeSignatures.find(ts => ts.tick === 960)).toMatchObject({ numerator: 3, denominator: 4 })
+		expect(re.unrecognizedSyncTrackEvents).toEqual([{ tick: 960, text: 'A 12345' }])
+	})
+
+	it('writing to .mid drops anchors (no MIDI equivalent)', () => {
+		// Anchors are .chart-only. Round-tripping through .mid necessarily loses
+		// them — the field is always [] on a .mid-parsed result. This test pins
+		// that contract so a future writer change doesn't accidentally smuggle
+		// anchors through as something else.
+		const chart = createEmptyChart({ format: 'mid' })
+		chart.unrecognizedSyncTrackEvents.push({ tick: 1920, text: 'A 12345' })
+		expect(roundTripMidi(chart).unrecognizedSyncTrackEvents).toEqual([])
+	})
+})
+
+// ---------------------------------------------------------------------------
+// unrecognizedEventsTrackMidiEvents
+// ---------------------------------------------------------------------------
+
+describe('writeMidiFile round-trip: unrecognizedEventsTrackMidiEvents', () => {
+	it('preserves Rock Band practice-mode assist-sample notes (24/25/26)', () => {
+		const chart = createEmptyChart({ format: 'mid' })
+		// deltaTime = absolute tick (per scan-chart's convertToAbsoluteTime).
+		chart.unrecognizedEventsTrackMidiEvents.push(
+			{ deltaTime: 0,   type: 'noteOn',  channel: 0, noteNumber: 24, velocity: 100 },
+			{ deltaTime: 480, type: 'noteOff', channel: 0, noteNumber: 24, velocity: 0   },
+			{ deltaTime: 960, type: 'noteOn',  channel: 0, noteNumber: 26, velocity: 100 },
+			{ deltaTime: 1440, type: 'noteOff', channel: 0, noteNumber: 26, velocity: 0  },
+		)
+		const re = roundTripMidi(chart)
+		// Compare just the shape that matters — tick + event kind + note number.
+		const mapped = re.unrecognizedEventsTrackMidiEvents.map(e => ({
+			tick: e.deltaTime,
+			type: e.type,
+			noteNumber: 'noteNumber' in e ? e.noteNumber : undefined,
+		}))
+		expect(mapped).toEqual([
+			{ tick: 0,    type: 'noteOn',  noteNumber: 24 },
+			{ tick: 480,  type: 'noteOff', noteNumber: 24 },
+			{ tick: 960,  type: 'noteOn',  noteNumber: 26 },
+			{ tick: 1440, type: 'noteOff', noteNumber: 26 },
+		])
+	})
+
+	it('is empty when no source MIDI events were on the EVENTS track', () => {
+		const chart = createEmptyChart({ format: 'mid' })
+		expect(roundTripMidi(chart).unrecognizedEventsTrackMidiEvents).toEqual([])
+	})
+
+	it('writing to .chart drops MIDI EVENTS-track events (no .chart equivalent)', () => {
+		// .chart has no concept of non-text events on its [Events] section;
+		// these are a strict MIDI-source concept. Round-tripping through .chart
+		// loses them — pin the contract.
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.unrecognizedEventsTrackMidiEvents.push(
+			{ deltaTime: 0, type: 'noteOn', channel: 0, noteNumber: 24, velocity: 100 },
+		)
+		expect(roundTripChart(chart).unrecognizedEventsTrackMidiEvents).toEqual([])
+	})
+})
diff --git a/src/chart/chart-writer.ts b/src/chart/chart-writer.ts
index f4fa682..85a89a5 100644
--- a/src/chart/chart-writer.ts
+++ b/src/chart/chart-writer.ts
@@ -82,6 +82,18 @@ function serializeSongSection(chart: ParsedChart): string[] {
 	}
 	if (m.diff_guitar != null) lines.push(`  Difficulty = ${m.diff_guitar}`)
 
+	// Round-trip any `[Song]` keys the parser didn't claim (deprecated
+	// Moonscraper / GHTCP fields — `Player2`, `HoPo`, `PreviewEnd`, `MediaType`,
+	// audio-stream filenames, etc.). Values are preserved verbatim: if the
+	// source didn't quote the value, we don't quote it here either. Consumers
+	// should treat these as opaque and never synthesize them — editors should
+	// discover audio via folder scan rather than trust `*Stream` values here.
+	if (m.extraChartSongFields) {
+		for (const [key, value] of Object.entries(m.extraChartSongFields)) {
+			lines.push(`  ${key} = ${value}`)
+		}
+	}
+
 	lines.push('}')
 	return lines
 }
@@ -96,6 +108,7 @@ function serializeSyncTrack(chart: ParsedChart): string[] {
 	type SyncEvent =
 		| { tick: number; order: 0; kind: 'ts'; numerator: number; denominator: number }
 		| { tick: number; order: 1; kind: 'bpm'; beatsPerMinute: number }
+		| { tick: number; order: 2; kind: 'raw'; text: string }
 
 	const events: SyncEvent[] = [
 		...chart.timeSignatures.map(
@@ -110,9 +123,12 @@ function serializeSyncTrack(chart: ParsedChart): string[] {
 		...chart.tempos.map(
 			(t): SyncEvent => ({ tick: t.tick, order: 1, kind: 'bpm', beatsPerMinute: t.beatsPerMinute }),
 		),
+		...chart.unrecognizedSyncTrackEvents.map(
+			(e): SyncEvent => ({ tick: e.tick, order: 2, kind: 'raw', text: e.text }),
+		),
 	]
 
-	// Sort by tick, then TS before B at the same tick. Duplicates preserved.
+	// Sort by tick, then TS < B < raw at the same tick. Duplicates preserved.
 	events.sort((a, b) => {
 		if (a.tick !== b.tick) return a.tick - b.tick
 		return a.order - b.order
@@ -122,6 +138,8 @@ function serializeSyncTrack(chart: ParsedChart): string[] {
 		if (ev.kind === 'bpm') {
 			const millibeats = Math.round(ev.beatsPerMinute * 1000)
 			lines.push(`  ${ev.tick} = B ${millibeats}`)
+		} else if (ev.kind === 'raw') {
+			lines.push(`  ${ev.tick} = ${ev.text}`)
 		} else if (ev.denominator === 4) {
 			lines.push(`  ${ev.tick} = TS ${ev.numerator}`)
 		} else {
diff --git a/src/chart/midi-writer.ts b/src/chart/midi-writer.ts
index f13a239..8e4a68b 100644
--- a/src/chart/midi-writer.ts
+++ b/src/chart/midi-writer.ts
@@ -237,6 +237,16 @@ function buildEventsTrack(chart: ParsedChart): MidiEvent[] {
 		}
 	}
 
+	// Round-trip any non-text events that were on the EVENTS track in the
+	// source `.mid` — most notably RB practice-mode assist sample notes
+	// (note numbers 24/25/26), plus stray sysex / channel / meta events an
+	// authoring tool happened to leave here. Events arrive with `deltaTime`
+	// already expanded to absolute-tick (per scan-chart's post-process);
+	// `finalizeMidiTrack` converts back to per-event delta below.
+	for (const ev of chart.unrecognizedEventsTrackMidiEvents) {
+		events.push({ tick: ev.deltaTime, event: { ...ev, deltaTime: 0 } })
+	}
+
 	return finalizeMidiTrack(events)
 }