Buster,
I do believe the reference to the "first over-flight" referred to the first of the Blackbird over flights.
The B-45 flights were earlier....and part of a multi-faceted over flight program that used various make,models, and types of aircraft.
Also....the anti-aircraft threat was much more sophisticated during the Blackbird's time in operation.
Also, the RAF crewed some U-2 flights as well, along with the Taiwanese.
https://fas.org/irp/nsa/maybe_you.pdf