I was looking around on flightaware and I happened to notice that, for example, flight BA2166 from Tampa to London Gatwick, for the past several days is recorded with call sign BAW61T instead of the "normal" BAW2166.
I had noticed something like that before (also on ATC feed), but this really got my attention. I tried to search around for the reason why a flight would not be called with what is really "its name" (BAW2166 in this case), but I did not find much.
Why do they use different flight numbers for one flight in the first place? As part of the previous question, does the format (00X, two numbers and a letter) and the letter itself mean something specific? What would the reasons be for doing it for so many days in row?
Thank you in advance for all your help!