If one wants to correct a mistake, he first names the mistake. Except for the Satanic verses, Muhammad doesn't do that. He basically says. if he contradicts himself, take the thing he said last. (Sounds like a politician, doesn't it?) Since Muhammad could not read, it was hard for him to remember what he previously said over 13 years. Actually, Muhammad says, if Allah does not get it right the first time, he comes up with something better. The problem is, neither Muhammad nor Allah can name all the abrogated verses. That is up to people who can read.
Whatever communications We abrogate or cause to be forgotten, We bring one better than it or like it. Do you not know that Allah has power over all things?
Surah 68:32..... (Sahih International) .......... Perhaps our Lord will substitute for us [one] better than it. Indeed, we are toward our Lord desirous."
Surah 16:101..... (Sahih International) ......And when We substitute a verse in place of a verse - and Allah is most knowing of what He sends down