Authorized to secret path but not thread id

[rnapier]

I am able to fetch a document using its secret path:

client.get_thread("...secret...")

This returns a payload:

{
    'thread': {
        ...
        'id': '...id...', 
        ...
    }
}

But if I use that ID, I get an authorization failure:

client.get_thread("...id...")

QuipError: 403: Not authorized: ...id...

The documentation indicates "Apps receiving URLs should convert them to permanent ids using Get Thread before being used." Is it expected that the permissions are different?