Only one time I can remember. I made a trade with a fellow MPL collector, my 1910 66RB for his 1910 66BN. After a year we were both talking and discovered we both missed our former coins. We just made the switch.......easy and painless. About 3 months later he sent his 66BN for regrading and it came back 67BN. Luck of the Irish.
no, but there is one I would. It was a Morgan with beautiful blue toning. I was close to loosing the house, needed to let it go. That is the only one I really regret. I would buy it back in a heartbeat, even at 2x what I got for it.