I read a couple if not more threads where people were asking whether there was a way for MusicBee to recognise a collection of lyrics they had collected before they started using MusicBee. It was not possible at the time but for those who are still interested, now it is possible!
When Steven developed this plugin I am sure he didn't have in mind for it be used this way.
All you have to do is to download the MiniLyrics Helper Plugin which Steven developed for the purpose of Minilyrics and MusicBee working better together.
All you have to do is to put the dll file to the "Plugins" directory inside MusicBee's own directory. If the plugins directory does not exist create it manually.
Now from within MusicBee go to "Edit> Preferences> Plugins" (the last tab at bottom). There you will find the minilyrics helper. If it its not enabled, enable it. Now, the second check box reads "retrieve and show downloaded lyrics file - configured in minilyrics as:", check that and chose the second option which read "specific folder" and chose the folder where you have your lyrics stored.
Just remember that the filename of the lyric files should be the same as those of the original music files.