To elaborate: MIDI reconstitution tends to fail with triplets, fermatas, swung rhythms and ritardandos. Other things that are lost are annotations like composer and lyricist, lyrics, tempo descriptions, precise time signatures, modal key signatures (other than simple major or minor), expressive markings, decorations, proper clefs, key changes...

Generally, MIDI is a poor medium for score exchange except for simple melody lines. Anyway, if you have a score source, it's so much quicker to translate it directly into ABC, with virtually no loss of information. You have to know ABC anyway, in order to clean up and supplement whatever the import process generates.