Of course the whole history of the Mach 3+ superplane is both murky and convoluted.
The whole line includes the single-seater CIA A-12 ***, prototype USAF interceptor YF-12A, drone carrier M-21 (the single engined D-21 drones were carried on the back) and the two-seater SR-71A, SR-71B trainer and "the bastard" SR-71C trainer kitbashed from the YF-12A and an SR-71 rear section that had been used for engine testing. The latter had a reputation for not flying straight. (grin)
Anyway, it amazes me that the whole SR-71 program came and went during my life.
Alas, I have never seen an SR-71. But SR-71B two-seat trainer tail number 61-7956 is at the Air Zoo in Kalamazoo -- I have yet to make a pilgrimage to see it.
And one of my favorite pictures of an SR-71B -- too big to embed here.
*** Adding to the confusion over the years, I often would read about the CIA A-11s. And wasn't A the designation for attack aircraft like the A-6 and the A-10 Warthog? As near as I can figure out, Archangle was the Skunk Works Mach 3 successor to Angel, which became the U-2 spyplane -- U for Utility to make the plane sound boring. By the A-11 design, the project was about to be greenlit. But they switched from a single tail to the iconic twin tails from the A-11 to the A-12 design, and the A-12 is what was built. So that's why there are A-12 and YF-12A actual aircraft.