I think they can be resold as long as it's not later than their expiration date, which is clearly marked on the tank and is, I believe, twenty years from the date of manufacture. I guess after twenty years they'll be shipped to LRD. There are two types either 3000 psi or 3600 psi which would blow a propane tank to bits pretty quick.
thanks for clearing that up for me. i just seemed to remember something about restrictions on the resale of tanks.