I would try use 'scan' on the remaining files on the left, and see if that matches a few more - but you'll probably have to do more manual matching on these, as 'scan' will ignore existing tags and just use the audio fingerprint (meaning songs will get matched to compilations etc much more often).
'cluster' > 'lookup' > 'scan' (on remaining files) > 'lookup in browser' (manually matching the very last files)
should hopefully catch most of your songs!
Anything left over you might have to add to the database yourself
I know I've already mentioned this, but I wouldn't save over your original files without at least double checking what Picard is doing (the gold CD icon is not foolproof!)