The Advanced 200 variant has a higher gross weigh and a longer range than the non-Advanced 200 variant. Visually there is no distintive feature between the Adv and non-Adv but as far as United is concernced, the one distinctive feature on the non-Adv is the extra emergency exit on the port side just in front of the wing. Adv 727-200's series aircraft don't have that emergency exit.
United's non-Adv 727-200's were configured in an all-coach seating for a high-capacity configuration, United used that config on high-density routes. That was the 70's. I flew in the early 90's on quite a few UA
727-200's, I cannot remember if those were Adv or non-Adv 200 series since the extra emergency exits were probably removed already. Hope this clarifies your query.