I thought Stratford was pick up-only towards Norwich, and set down-only towards Liverpool Street. Am I mistaken? Also, does it only apply to intercity services? I've certainly used the 720s to get from Stratford to Liverpool Street to grab a seat on the next Norwich service before it gets busy. Definitely the preferable option to getting a Clacton/Colchester Town service and changing at Chelmsford or Colchester. Elizabeth Line and the tube are out of the question because GA travel was free for me at the time.
EDIT: The timetable says pick up-only on northbound trains, set down-only on southbound. It also seems to only say Ipswich stoppers have the same restrictions, and other services operated by 720s don't (except in the morning peak and some odd edge-cases at night). I probably never boarded a set down-only train, they certainly weren't advertised as such!