It has. Just last week. The house I appraised had a non-permitted room in the garage which I didn't count in value. It was a three car garage. The cost to remove the interior walls was less than $500 - it was really a make-shift type of office, but functional. I commented in the report all about it and how it is not considered in living area and not in value and that the cost to cure is less than $500, but then in the sales comparison approach I gave value for a 2 car garage only. I fell asleep on the report actually. I had to finish it before taking my seven year old son to the hospital (he's okay now), and the rush made me do something stupid that was picked up on.
[1] I changed the report, increased the value, stated the error that was made and how it was corrected in both a cover letter and in the addendum, and gave it a new signature date.
[2] Whether the scope of work changed or not, I don't know. I think I was still asked to appraise the property for market value following the client and Fannie guidelines and that remained the same. My best guess would be that I was supposed to be accurate and instead of the scope of work being changed, it wasn't quite lived up to perfectly the first time, so it is more of a correction to comply with the original scope, than a change in the actual scope.
I could be wrong.