This. When I was a kid (in the late '60's/early '70's), I would never have dreamed of cutting a coin out of a proof set and putting it in an album. That attitude was common enough that many albums simply didn't have a spot for proof-only issues (say, S-mint dimes from 1968 onward). If you wanted spaces for those coins, you'd have to buy an album "including proof-only issues". Of course, my budget limited me to the cheap Whitman folders, which didn't really offer adequate protection for proofs anyhow.