"In all those years, did you typically operate at upper-altitude limits for weight and available power where this kind of thing would have automatically been a problem? If the oat did make a jump, would've you necessarily noticed?"
With the Atlantic crossings, we would go to where assigned and then ask for the highest (ride permitting) altitude we could handle based on the "Box" and a bit of common sense. As I said I have seen 3 and 4 degree changes but never 20 to 30. I do tend to glance down at SAT and TAT and, now in Saudi, ISA plus, especially at the first indication of a ripple.