I add tags to m4a file via exiftool:

Code:
exiftool -ItemList:year=1999 -Keys:year=1999 -Userdata:year=1999 file.m4a -overwrite_original
MediaInfo shows the year info like this:

Released date : 1999
yrrc : 1999
com.apple.quicktime.year : 1999

But Edit ID-Tag shows nothing:

https://i.imgur.com/9ABbeAX.jpg

What is the problem?