For those airlines that do report tail numbers, almost all of the flight numbers shown are different than just tracking without a tail number. Here’s an example. I saw an A320 numbered N108UW on July 17th landing at ORD at about 6:42pm. When I look up ORD arrivals, I see US Airways 703 from PHL, an A320, shown at that time. But if I put in N108UW in the tail # tracker, I get a page of tracking for N108UW/AWE829. Looking down that list, it does show that flight from PHL to ORD on July 17 at the same time. So, which is the correct flight number - 703 or 829?
At first I thought maybe there’s a difference due to aircraft swaps but this pattern repeats for almost every plane I have spotted - United and Air Canada as well. C-GSJB has two flight numbers associated with one route on July 17 from YYZ to ORD. I don’t know why that happens.