On Thursday night my flight showed canceled on the app (no announcement from the GA) so I walked over to the monitor at the gate and it showed canceled. So I got on the phone with the 1K line and the CSR said it didn't show as canceled to him. I told him I was staring at the screen at the gate and it showed canceled. He refreshed and "suddenly" it was canceled on his end. On top of that, the GAs didn't actually announce to those in the gate area (who may not have been paying attention or thought it was accurate) that the flight had been canceled for at least another 5 - 10 minutes (thought not entirely surprised because this was the UAX part of IAD where they operate 20 flights from one "gate"). Even better as I'm on the phone with the 1K line after it's been announced I go up to the counter (they weren't processing flight changes b/c it was a multi-departure gate) to find out about bags and the GA wasn't even aware the flight had been canceled.

Moral of the story is YMMV and your best bet is to check all of the different options since the technology powering each seems to be different and doesn't seem to sync up in any sort of logical / efficient way.