Why would TR 8R know
>what Finn looked like?
>that he was a traitor?
I can get that there was some sort of bulletin or memo that was sent out, but that would be pretty stupid because it would show that any stormtrooper could defect and have a sense of identity. Just stupid really.
They must spend some time together without their helmets on. Eating meals in the mess hall? Showering? Getting ready for bed? I don't think it's that silly that someone would recognize him.
I really like this theory.
I won't be surprised if Disney canonizes it, even if only to cash in on TR-8R's online popularity. Given the precedent set by the old EU, it's no stretch to assume that every random stormtrooper has a backstory.
A sense of camaraderie and a willingness to fight for the man next to you is one of the greatest assets that a soldier has.
Presumably it's things like that that make kidnapped-and-raised-from-birth stormtroopers superior to clones or battle droids, otherwise the First Order would be using them instead.
I'm sure all the stormtroopers know each other.