I've recently started adding full dates instead of just the year.
After some experimentation, I arrived at this method and wrote this virtual tag to format dates that you might find useful.
$IsNull(<Year>,Unknown,$If($IsMatch(<Year>,"[0-9]{4}-\?\?-\?\?"),$Left(<Year>,4),$If($IsMatch(<Year>,"[0-9]{4}-[0-9]{2}-\?\?"),$Date($Replace(<Year>,-??,-01),MMM yyyy),$If($IsMatch(<Year>,"^[0-9]{4}$"),<Year>★,$Date(<Year>,d MMM yyyy)))))
It will display date tag values stored in the format
yyyy-MM-dd
as
d MMM yyyy
For older or obscure albums where I can't find the month or date or release I substitute question marks in the tag value and they will be omitted from the formatted value. MusicBee's
$Date function defaults to the first of the month if you give it a date in the format
yyyy-MM, which bugged me.
Finally, if it's an album that I haven't yet looked up to replace the older four digit year with the full date, it will show a star next to it to remind me to do that (and to distinguish it from an album that I couldn't find a release month for).
e.g.
The date values for these five albums, left-to-right are:
1989-10-20 1994-03-?? 1999-??-?? 2000 <No year tag>

(Yes, full dates are available for all of these albums - I've fudged them for demonstration purposes)
Disclaimer: I tag everything using Mp3tag and using full dates or non-numerical characters in year fields may break compatibility with other programs or apps. I haven't had any issues but YMMV.