Bullock wasn’t with the GCPD back then. Jason’s death occurred when he was a Checkmate agent. Bullock of course spotted the difference between Dick and Jason, as did Gordon, and it was addressed expressly in the books.
It never became public knowledge that Robin had died. Superman told Bruce he’d “read on the telex” that Jason had been killed, but even he had to ask Bruce if Jason was Robin.
Cheers - CL