I think all this is a myth as long as you don't move out of state. The ATF would like you to notify them if you relocate but I don't believe it is law. Please correct me if i am wrong?
I believe you are wrong, at least from what I read and was told by the ATF Agent. When you have a tax stamp weapon the ATF has the right at any time to show up and request to see the weapon and make sure everything is secured and in your possession.
This is why I was told that the address has to be updated at all times.