That depends on your settings, the default setting does need an updated timestamp to re-read a file.

As there's no batch method for lyric addition in Media monkey or incrementing thru each song to add lyrics.
With 41,000 files incrementing one by one wasn't a serious option.

I started using Mediahuman lyrics finder. It does a halfway decent job of finding and inserting lyrics into files.
Imagine my surprise when Lyric Finder said it had found most of the lyrics and updated the files, yet when I re-scanned folder with Media Monkey, it failed to pick most of the newly added lyrics.

So I used Mp3tag on the updated folder and files and saved all the tags from MP3tag.
Then when I re-scanned the folder with Media Monkey it found and imported the lyrics.

I learned that Lyrics Finder did not update the file date when placing lyrics in them.

My assumption is Media Monkey fails to recognize new lyrics in a file as enough of an update to re-import the file data unless the file modified date has changed.

If there is some other flag to recognizes just updated lyrics, it is not triggering effectively.

The work around is messy and I really didn't want to re-save and re-date all of my files to get Media Monkey to bring in the lyrics.