Good question. I know aadsas is very clear about the importance of signed letters, however it doesn't seem right if one of your recommenders makes a mistake and forgets to sign the envelope.
You said that they weren't sealed...so that means you could have read the letter??? I think some schools might ask if you have read any of your own LOR...so that might be a problem if they ask. Has anyone else heard that you are not supposed to read your own letter?