You missed all of my edit.
Anyhow, the creator of the works would have to prove that the thief is a liar. I don't disagree that CURRENTLY the safest way is to register the works, I am simply saying that an intelligent infringer could potentially make that process pointless. If the infringer did file before you, then a wise judge would have to consider further evidence to settle the dispute. If the infringer could not produce the files then he has nothing.
In order for someone to change the dates, then they have to have access to those files. If he doesn't know where they are kept and has no access to them, then he has nothing. Besides, anyone who really wants to protect their work should not keep all of it in one place. I make copies of my projects on external drives (while the project is still underway) that will never get deleted for more space and then I delete everything from the project drive to make room for the next project. You can't hack what's not connected to the computer and no common infringer is going to access a studio computer, or secure location (safe deposit box, or safe stored in a secret location) to steal the files on a hard drive. If he even tried he would be facing much stiffer penalties than copyright infringement.