So what were nos playfields like when the games came out. Were they just dimpled?

EMs and SS up to the mid 80s - No such thing as "NOS". They were use in the production run. NOS was more a case of "leftovers" or "defects". Factory employees and executives often took home playfields and backglasses. Backglasses were kept as a "spare part" which nicely fits in with what we call "NOS" today.

Later machine - mid 80's onwards - Greg is correct as far as I know.