Not in a mint set but in a proof set I have. Sold a 1969 proof set to a customer, he came back the next day wanting to exchange it because it was defective. The quarter was about a 10 to 15% clipped planchet. Told him I would be very happy to exchange the set, but that the set with the error in it was worth well more than what he had paid for it so I was willing to buy the set back at 10 times what he had paid and throw in a replacement set. He was happy, kept the error set and bought a replacement set.