I have not chronographed any of those shells but suspect that you are correct about the muzzle velocity being lower at colder temperatures than published.
If I remember correctly, those published velocities are at 70 degrees. I'm not certain how much or what the percentage is that they drop at different temperatures however.
You've pointed out another good reason to try your shells at different temperatures and weather conditions. We don't often get to hunt under those "ideal" conditions of 60 -70 degrees, with low humidity and no wind, do we?
"If he's out of range, it just means that he has another day and so do you."