Proof is actually a term to denote how the coins are struck, the proof coins are struck with more pressure , with (usually) more detailed dies and specially prepared blanks. The difference between the proof coins and their business strike (mint set) counterparts is very noticable side by side. If you want the "business strikes" of coins for a particular year you can get the mint sets or singles.
I guess my thinking is that the P example from before 1968 would not look quite right next to the D example in a collection if it were proof- so yes by all means get them all !! That would be a P,D,S, and proof example of coinage from that year . That would be complete set for a year IMO not including any errors or varieties.
Not all years have four sets a year either, after 55 there are no S mints until 68, and 65-66-67 have no proofs and no mintmarks- only five coins for that year I guess ten if you get coins from circulation and the Special Mint Sets
I guess my thinking is that the P example from before 1968 would not look quite right next to the D example in a collection if it were proof- so yes by all means get them all !! That would be a P,D,S, and proof example of coinage from that year . That would be complete set for a year IMO not including any errors or varieties.
Not all years have four sets a year either, after 55 there are no S mints until 68, and 65-66-67 have no proofs and no mintmarks- only five coins for that year I guess ten if you get coins from circulation and the Special Mint Sets



















