Question: The rounds tested @ 70 vs rounds tested 45 degrees, were they loaded under the same conditions, IEI can't help you much, but I've wondered the same thing as well?
Something I've noticed also is: I've had a few guys recommend one freezing or cooling down their ammo in order to find out how your powder/rounds will act in colder temps... and I've only tried it once thus far, but it didn't really tell me much of anything. Shooting ammo that was reading 45degF per a temperature gun, while in the high 70's, was nothing at all like the results I got when actually shooting in conditions at an ambient ~45degF... maybe it works for some, but for me it didn't help at all really (except now I have some data on shooting 45F ammo in the upper 70F's).
I think you can only glean so much without actually having the ambient conditions in place...
reloaded at the same time, if not was Temp and RH the same for both rounds. Reason I ask is that there MAYBE an additional factor - amount of water vapor trapped inside the case which may influence pressure. I repeat MAY,
From a physics point of view: I do know that if you increase the amount of water vapor, all other factors the same, pressure would increase as water vapor trapped increases. The amount of water vapor trapped inside a case. Effected by Temp, RH, Barometric pressure, and effected Most by % filled (PS even a compressed load will have some water vapor unless RH = 0). How much I can not say, it may be inconsequential, and just food for thought.