I recall a UX flight ex-IAD where I stopped by the terminal C RCC and was informed by the agent, "You know, your flight is boarding right now, and it's in a different terminal (A)."

I looked at my BP, said, "But boarding isn't scheduled for another 40 minutes."

The agent said, "The system says they're already boarding."

I rushed over to A, and sure enough, they'd already boarded everyone, and the GA was a bit put out that I'd "delayed" them (we were still at that point something like 27 minutes before scheduled boarding).