Brian carried this Stratocaster as a backup on tour around 1974, which was before he had any replicas made of the Red Special.
Based on the maple neck and the headstock shape, the guitar was probably made sometime in the 1970s. Obviously, Brian started using it around 1973, so it had to have been made before that. The guitar also seems to have a clear finish, because the wood grain seems to be visible on some of the footage.
But, aside from what can be concluded from the photos and the footage, not much can be said about the guitar. It’s unknown whether Brian still has it, or whether he got rid of it after 1974.
There were actually two Stratocasters in the 70s: the yellow one in this photo was probably borrowed or rented for that mimed performance only; Brian’s actual guitar was black, and he had it at least since July 1973 (he mentions that in his first interview ever, and it can be seen in the background on the videos for ‘Liar’ and ‘Keep Yourself Alive’).