You can set a highlighting rule to show which tracks are updated. I use one for lyrics and it shows at a glace which tracks don't have lyrics. And when updating lyrics, if lyrics are found for the track(s) the highlight goes away.
Preferences > Tags (2) > tag handling > highlighting > define rules
Note that you'll also need to display the 'highlight' field in the tracks view so that highlight shows.
While that IS a creative method to let you know files that don't have Lyrics, your solution STILL presents the same problem I'm trying to fix.
As you stated the highlighting is "removed" automatically when lyrics are found. So, there's no actual way to "track", see, review, and edit these files. They just disappear into the void of files with lyrics.
So, either way, we need the functioning I've addressed. Though, I appreciate the additional method to see what files don't have lyrics when you're looking at your list.
Of course, it doesn't really help me, I don't use the Track view. So, for me doing the "find missing lyrics" function, which then lists them out is easier.
Now, obviously, in time a person will know what files don't have them, but we need a better system, something like I've stated.
Especially since what I'm requesting doesn't "just" apply to Lyrics, but Tags also. You can create a "list" showing what files are missing tags, and we would have the same problem. When they are updated they just "disappear", thus it's important we are able to review what's been updated.