That what annotations and edit notes are for. 
Iād personally probably just put it in an edit note in this case, but it might also be useful to have an annotation saying something like āTrack 55 is a āhiddenā track that doesnāt have a title on the cover or in the booklet. Title is known due to ā¦ā.
Right, but annotations and edit notes donāt show up in tags.
Iām coming into this discussion late in the game, but my thought is that with hidden CD tracks, we should name them:
[hidden]
and then if the name becomes known, we update the track name to:
[hidden] track name
Here is a good example:
has a track 5 on it that has been named Love Song because the name became known later under another release for another album (as I recall). However, the jewel case contained no documentation about any track #5. I proposed updating to:
Love Song (Untitled)
But, was informed by @Rogee about how Untitled has a special meaning to MusicBrainz. Okay, I get that and Iām good with that. But, I still remember listening to this CD when it first came out and getting surprised by track #5. That is the usual response for any hidden track and I think we really should try to help those that find this album on Musicbrainz to know of the artists intention to surprise the listener. I think the solution of using a [hidden] tag as the default prepended value for the track name helps to do that. Any thoughts from folks?
If you know the name of the track, then you can name it. Stick a note in the annotation to explain the source of the name. I also add notes about the gap size too.
No need for āuntitledā, just give it the name.
See Nirvana \ Nevermind for an example: https://musicbrainz.org/release/8e061dc4-790e-4587-ba53-011e7852f88d
Well, Iām thinking about those that use Musicbrainz to update their music files with ID3 tags from this online catalog. They wonāt see the annotations in their libraries. They will just see a track number and a name for it. Iām looking for a way to capture the intention of the artist when they released the CD. If you look back at my last post, Iām suggesting this format:
[hidden] track name
It letās folks know when they are looking in their libraries on whatever music management software they are using (e.g. iTunes, Plex, whatever) that the artist intended this track to be a surprise. It gives back some of that feeling one had when hearing the CD for the first time. It also allows a way to provide more accuracy about the album in total. One can still add annotations when adding or updating the track to the Musicbrainz database, but that is more of a historical note for those perusing the Musicbrainz database, not for those listening to the music via their favorite app.
Here is an example of an edit Iāve done to an album that uses this format, so you can see what it looks like: