Many time the composer field is left blank when i do an automatic lookup on musicbrainz. Can this software search allmusic.com for this info?
blank composer info
No, it does not query allmusic.com for any information.
If you plan on adding this “manually” - make sure you edit the MusicBrainz database instead of your local files only - this way we don’t all have to do it manually 
Sometimes the info is conflicting depending on which source you pick. i would hate to post the incorrect data and have that passed on.