Is EF inventory still real-time (or close to it) in the last few minutes before a flight?

I was on ORD-LAX last week and second on the upgrade list; it showed J2. I approached the GA at T-10min and asked if she had processed the list. She said she hadn't...I said something like "OK, well let me know...looks like it's J2 and I'm second on your list" and she immediately (without looking at anything) said "oh, no you'll be 3rd now, there's someone else ahead of you that isn't on there." I of course reacted incredulously to that, which caused her to change her story to "somebody just bought a full fare J ticket at the airport ticketing counter." My response was "uh, I'm looking at your inventory and it still says J2" but that just kicked off an accusatory conversation like I'm not supposed to have that information. In any case, she only cleared one person off the list, and they did indeed fill all the seats. I'm still suspicious (paranoid?) that they snuck some friend in, but obviously I have no way of knowing.

So I guess my question is, how far can I trust EF in a situation like this? Is her story (full-fare in-airport purchase that didn't deplete the EF inventory) plausible? I know that I've been on the phone booking a flight with AMEX and I can refresh my search and see the inventory depleted immediately. But then I also know that the flight in question still showed J2 after they cleared the gate upgrade, so it wasn't accurate at that point.