Correct, the only evidence I've seen here is anecdotal of seeing a BE passenger's BP (with group 5 boarding) when they sit in E+ while the flight later goes out with empty E- seats. Which 1) doesn't guarantee that the BE passenger didn't choose to buy up to E+ after check in or 2) that there were E- seats open when the E+ seat was assigned (as E- seats can open up late in the boarding process when people get offloaded). The other situations that were provided to "show" this was happening (seeing passengers on the standby cleared list into E+) have been refuted, including by people who work at UA, as BE seat requests don't show on the standby clearance list at United (unlike Delta, where the gate display is a seat request list and does show BE seat assignments).