I use the following 'matrix' to help me find any missing tags.
Someone posted this a long time ago on this forum but i can't remember who it was.
You can use this in facets:
$if($strcmp(,$if(%artist%,,A)$if(%title%,,T)$if(%album%,,a)$if(%comment%,,C)$if(%tracknumber%,$if(%totaltracks%,,#)$if($meta_test(album artist),,R),)$if(%genre%,,G)$if(%date%,,D)),Ready,$if($strcmp(,$if(%artist%,,A)$if(%title%,,T)$if(%album%,,a)$if(%comment%,,C)$if(%tracknumber%,$if(%totaltracks%,,#)$if($meta_test(album artist),,R),)$if(%genre%,,G)$if(%date%,,D)),Ready,$if(%artist%,,A)$if(%title%,,T)$if(%album%,,a)$if(%comment%,,C)$if(%tracknumber%,$if(%totaltracks%,,#)$if($meta_test(album artist),,R),)$if(%genre%,,G)$if(%date%,,D)))
You'll soon get the hang of what all of the placeholder stand for.
Thanks to the original poster, it is absolutely brilliant, i never could have come up with this myself.