My rule, tough cheese! Are we really this fussy when it comes to trains? No we're not! If you couldn't quite ID something and you asked on the TOPS Request Thread for some gen, then someone says "It's showing Xyz". As far as I'm aware most people at least would be happy to accept that as fact, even if TOPS/Genius/TRUST/gen groups/word of mouth is far from infallible!
It does help G-FBEK was the only plane in the sky at the time for many miles around, there could be no mixing up one plane with another! Now if I was sitting here, going through Flightradar24's app and just ticking off what it said was above, without even seeing a plane in the sky (due to cloud cover or just not looking!) then I could understand the raised eyebrows.
As I say, if someone was to give you the numbers of whatever was in a rail yard, you'd take that without going and seeing with your own eyes each and every number, why not this way? Don't get me wrong, I won't be filling my AFQR entirely this way (that's not fun!), but it sure helps!