"Original" means that it has all the original parts that were put on it when it was made. A percentage of original suggests how much of it remains unchanged. If the safety broke and was replaced, it is no longer 100% original, but you could describe it as 99%.
"Correct" means restored to look like an original. All the parts are from the proper time period for the serial number of the receiver, things like the correct stock markings and parts numbers. "Mostly correct" means just that, most of the restored parts are the right ones.
Many of the late SA's examined and sorted at
CMP
during the
GCA
convention appeared unfired, but the whole trigger group was HRA, obviously switched with one of the mint late HRA rifles Greece had. It would be no trick at all to find a correct SA trigger group and put the rifle back the way it was.