You can plug all the mathematical data in you like, but the original posters quote, with regard to temperature effects and much older mach indicators are quite correct....of course, new(er) pilots simpy have no knowledge of this as they no doubt didn't fly any of these older aircraft.
Aren't we smug?
I know a captain in a 747 classic who's 25 years old. When I was his age, I was flying 40 year old equipment. The age of the pilot, and even the recency of the pilot, isn't really relevant to understanding "old" technology.
So far as mach number...mach being a function of temperature...temperature variation is relevant, and does apply.
Next we'll probably hear that if it's not an L1011, it's not really an airplane...