That particular version was called the M-21, not the SR-71.
There were several variants of the Blackbird. The version that carried the D-21 drone was a converted A-12 redesignated as the M-21.
You can read about Blackbird losses here.
Blackbird Versions:
A-12 single seat reconnaissance bird for the CIA, code name Oxcart.
YF-12A two seat interceptor
M-21 two seat drone carrier for the D-21 drone.
SR-71 two seat reconnaissance bird
There were a small number of Blackbirds that featured a raised rear cockpit for pilot training.
Here's a great website for Blackbirds, complete with the declassified pilot's manual. One of my coworkers was an SR-71 RSO for 5 years. He has some good stories but has to be careful what he discusses because a lot of it is still classified.