I was a 3P, then 2P and a 1P for nearly 2.5 years before .bomb decided to let me choose E+ seating.

Then, one magical day, after about a dozen trouble tickets with UAL, it finally started working.

The way to test, choose a flight like 6-8 months from now, on a popular route (say ORD to SFO, etc) and see if there is E+ (or give me the flight you are booking, and I can check for you)

Bill