I'll go further and say that it would be much simpler if we could just download small playlist files for the ranking charts, throw them in the Songs folder, and have them be treated as Folders. Right now, with three different charts it has become an extra pain to organize.
favourites A is a list of md5 hashes of each .osu file in your favorites(so 1 hash per difficulty)
if you simply construct a dictionary of each .osu file to its respective hash in your songs directory it would be easy to cross reference them and therefore obtain the desired metadata
basically goes through your favorites a or b and shows the associated song with it (same song may be shown multiple times because of multiple difficulties) note it only works with ranked maps