Actually you are both right. sort of. There were twelve design passes on the SR71 and A12 was the last.
A12 was presented to the CIA, which ordered 12 of them in 1960. The first SR71 was presented around 1962. It was an updated A12, which carried camera gear which could cover the peripheral view, which is the primary difference between the first SR71 and the last A12. The A12 only had straight down view cameras.