For the "Year" tag, I always use the release date, accurate to the day wherever possible, with the exception of live bootlegs which are tagged with recording date.
I then have a custom tag defined as the ID3 standard "Original Date". I use this field for compilations where I put the year of original release for each individual track.
I then complicate all this by having this Virtual Tag which takes both of those fields and gives me the release date of each track - $IsNull(<Original Release Year>,<Year (yyyy)>,<Original Release Year>).
I'm currently trying to find a way to create something similar to the Decade field using this virtual tag.
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