You are right about this - though I think we have another issue to fix.

compatid3.py does indeed split the date in this way when saving and so I will remove date from this code. Original date can still only be year though.

However I need to check what mutagen does with date when the file is read. Picard doesn't handle TYER explicitly (TDRC is the tag for date), and dates are read in from id3v23 files - and see if anything needs fixing.