I think you are correct. If I'm not mistaken, however, some locations allow you to print off a backup ballot, fill it out, and turn it in. This invalidates your original ballot, which was presumably lost before it got to you. I'm sure there is a mechanism in place to compare signatures to the database to throw out a bad replacement ballot if anyone nefariously tried to take over that system.  I do know that they won't count the original ballot if it arrives or not - I believe they invalidate it the moment you print out a new one.