I dont think dogs forget when they do something bad.. thats why the act guilty for in the first place. i think that 'dont punish your dog if you dont see it doing at the time' is bull,, and wrote by a dog. LOL

one time we came home from shopping,, and my bridge girl Muffin greated us at the door with pinned back ears and non wagging tail. (a sign of guilt) from her...
and sure enough.. she had chewed up a bunch of stuffed toys that were up on my bed and she knew she did a no no.. or she woudlnt have acted guilty.

so i dont think dogs forget.
though i do no punish for booboos.... unless i do see them doing it..
but i still dont think they forget.. LOL