The "lift coefficient" $C_L$ can be very different for one specific aircraft at different speeds.
According to this article from NASA about the lift coefficient:
So it is completely incorrect to measure a lift coefficient at some low speed (say 200 mph) and apply that lift coefficient at twice the speed of sound (approximately 1,400 mph, Mach = 2.0). The compressibility of the air will alter the important physics between these two cases.
Joseph A. Walker flew those two spaceplane flights that qualified him as an astronaut under the rules of the U.S. Air Force and the FAI.
Could have been or has been the lift coefficient calculated from the collected flight data from those two events?