Do you mean it gets the actual notes wrong, or that it gets the key signature wrong? You appear to be a bit confused between keys and chords. The key of C major and of A minor have the same key signature (no sharps or flats) and the same set of chords fit straight into both keys - Am, C, Dm, Em, F, G. There's no way of telling whether something's in C major or A minor except by context. "Converting" something from the key of C major to the key of A minor means leaving everything as it is. If it's been put into Eb major instead of A minor, it just means (if it's got the actual notes right) there's a load of unnecessary natural signs on the score.