if you look at coin price guides, they generally list the collective values for individual proof coins higher than the complete proof set. I've never really understood the concept behind that idea, but it explains why dealers often have individual proof coins for sale. They break the sets up to sell individual coins for maximum profit. Some collectors prefer individual coins because they are easier to store than the bulky complete sets. Proof sets are assembled at the mint by employees wearing special gloves to prevent their skin from coming in contact with the coins, causing finger prints or tarnish. When I see an individual coin sold as a proof, I don't doubt it came from a proof set, but I wonder if the same precautions have been taken when putting the coins in a 2 x 2 holder.