Found this thread after encountering same issue.
My folder structure follows this pattern where possible: %ARTIST% / %DATE% - %ALBUM% [<differentiator>] [/CDx] / single flac or separate tracks.
Everything I have on CD's is archived as a single FLAC together with a cuesheet in same folder as the FLAC.
The remainder is, where possible, in separate files, also with a cuesheet in same folder.
For some reason I never had this issue in FB2K < 1.6, I had a ColumnsUI column in my playlist view which pulled discnumber and tracknumber just fine if there were ./CDx/ folders present (otherwise it would just be the tracknumber).
All of a sudden, while cleaning up some files, I encounter a situation where the cuesheet entries in the playlistview didn't show the discnumber... still can't understand why, as I still have cuesheet entries from way back where they DO show.
I finally gave up trying to find out why and just went with titleformatting.
$if($or($strstr(%path%,'\CD'),
$greater(%discnumber%,1),
$and(%discnumber%,%tracknumber%)),
$substr($directory(%path%),3,$strrchr(%path%,'\')))-,)
[$num(%tracknumber%,2)]
This only works if you have each disc of a multi-cd album in it's own CDx folder.
I just gave up using DISCNUMBER for the display and instead substr the number part from the containing CDx folder to construct the DISCNUMBER display. So at least now my multi-disc entries show a DISCNUMBER in the playlist views, regardless if it is generated by a cuesheet or just the actual audio files if there's separate tracks instead of a single archive file..
So, yes, I vote +1 to have DISCNUMBER and TOTALDISCS retrievable when reading a cuesheet. As it stands now, in a library where there's a mixed occurence of both single archive files with cuesheets and folders with just separate tracks, using DISCNUMBER and TOTALDISCS in playlistview columns, besides the already mentioned other uses in the other thread, is pretty much impossible. Seeing as you need to jump through hoops using titleformatting functions when there's a cuesheet present, it's pretty much useless to even fall back to DISCNUMBER and TOTALDISCS when there's no cuesheet.
The argument that this way you have a workaround is just a lazy man's answer. These tags exists for a reason, one shouldn't be forced to bend over backwards trying to get the same information because some filetype doesn't support the use natively.