Back to the OP, the scanner has two parameters controlling this. The first is the threshold value - if a mark is darker than the threshold - it's scored. This value varies from machine to machine. It can be set manually or automatically by a box on the scanform itself. The next is the difference value - if the scanner sees two marks, it compares their darkness. If they differ by more than the difference value, it scores the darker, if they don't vary enough, it outputs a multiple mark character. It is very unlikely an erased mark would be dark enough to be over the threshold AND close enough to the actual mark. I can't speak for LSAC, but normally when working with a scanner you set the threshold fairly high to handle stray marks, erasures, etc. and then you set the difference pretty close so you will take the darker mark and not kick out an error. You're just having normal post-test paranoia.