Early SOCOM 6920 lowers had the firing selector stops shaved off, "C" stamps where appropriate (e.g. BCG, upper receiver, barrel), and all the info (e.g. serial#, pony logo, etc.) was roll marked. Newer SOCOMs have the selector stops, markings are engraved instead of roll marked, and Colt's CAGE code is on the upper receiver and barrel instead of the former "C" stamp.
Just depends what you prefer. I have both styles, but after getting used to the newer style w/ selector stops, I think I prefer the newer one. My eye notices if the stops are shaved before I notice whether the markings are roll marked or engraved. Now, they just look strange to me if the stops are missing! I do like the individual character that roll marking can give a rifle compared to the neat and boring engraving, but I'd still rather have the selector stops.
At the end of the day, if it's a Colt, I'm happy.