They made proofs in Philly before they went back to SF. If the luster is there, details, thick squared rims, and a LOT of step detail, it is probably a proof.
Inspector? Tone down the lighting some. Maybe repost another Pic? If it was a proof, it's an impaired one. Time will tell.....
Here are some new photos. I don't think it is a proof. In hand you can see the mirror like surface. Very nice for a roll find. I found a 1961 D in the next roll.
I find a lot of older coins that appear MS. No marks on the surface. Just like they came from the mint today. I wonder how that can happen?
Hard to tell from photos I would have to see it in hand. Try natural lighting. The photos are very washed out. I find older coins from time to time that are MS or very close to it. They must have been dumped from someone's collection and you got them before they circulated too much, because any time in circulation will ding them up and tone down the luster quickly.
Your new photos show it’s not a proof. It was probably made by a newer die and saved since its was minted. Nice roll find!
That's just a really nice PL in my opinion. Maybe they forgot to punch on the S mintmark on that one lol.