I could be wrong, but I though everyone who bought early Primes had the buyback option, and everyone who exercised the buyback option also had the "reverse" sale button.
I spent enormous amounts of time clicking through ZenCloud at the time when all this was going on and I could never get the buyback to work for me. I think it only worked if there was someone willing to buy your primes at full retail? I don't remember now, it was so convoluted.