Mysterious IDv2 tags that MP3tag can't find?

So here's the skinny.

I've got a whole stack of files that some genius tagged like this:

Should be basic to go into mp3tag and have it batch-overwrite "various artists" in the artist field with the actual artist name from the comment field, right?

However, when I load the file into mp3tag 2.72... can't see the comment field. It sees the other fields, no problem. But not comment. I've been poking at this for a bit now, trying various permutations of fucking with the tags, and mp3tag just continues to miss the field completely. It's entirely possible that I've missed a configuration option somewhere, but this seems like the sort of thing that the software should pick up by default. I dunno.

Anyone got any advice?

You should check the settings in
Read and delete all tag versions
Write only V1 and V2
If you have problems with sometimes visible and sometimes invisible fields, play around with settings for reading APE - perhaps (overwriting) data is stored there.

Definitely hadn't thought of that, giving it a go... luck. Thanks, though.

What do you see when you press ALT + T or

View - Extended Tags

If you still don't see it, care to upload one of these file so we / Florian can have a look?

Now we're getting somewhere. It's apparently filed what I see as a comment field outside of mp3tag as "COMMENT MUSICMATCH_TRACKARTIST"

So that's the field that has the info I need to replace the ARTIST field with.

e: Now I've got a column I'm oh-so-cleverly calling comment2 that shows that field. Now I just need to find a function that'll let me punch in the data from one field to the other.

Use an action of the type "Format value" for COMMENT

You can try the same with the function Convert>Tag-Tag

Tag to tag has properly moved the data into the artist column.

I think we can mark this one solved. Thanks for helping out, everyone.