As COINMAN1 said, some say Proof is not a condition. And I am one who would completely agree with that.
For the most part, modern proofs should typically grade above a 60 (MS on regular coins); however, an impaired proof is one that has been circulated. Take the one in this link, for example:
https://forums.collectors.com/discussion/1003505/show-me-a-circulated-impaired-proof
The coin was graded Proof-45 (so... EF).
And because of impaired proofs, I like Numista's current format.