I personally work from the written listing contract date, even if the property will not go in the MLS for a week or two because of things such as staging, etc. However, since our MLS service requires all listings to be entered into our MLS within 3 business days of a signed listing agreement, I also need to have a MLS waiver signed if the listing is not going into the MLS right away. I have never heard of having a "final" copy of a listing agreement esigned after the seller has already "wet signed" an original listing agreement.
If your main concern is that the ending date of the listing also changed, that could easily be fixed by doing a written amendment to your listing agreement. Listing agents want to keep the path of communication open with their clients, so please bring this up with your agent. It could be a simple misunderstanding that is easily remedied.