That's a good find!
I think you interpret correctly, laminar b.l. being worst case by 1 degreeC, and likely first half of wing chord nominally laminar in cruise, so TAT - 4C
Agree, OAT/SAT == Kinetic Temperature in first results table = -56.5 C
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Boundary layer Cf and thicknesses are interesting...
An old rule of thumb was that the b.l. thickness on a Spitfire wing at 400mph was 1"
This gives that for a 6 ft chord ref length at 20,000 ft...