I've noticed the same thing. Beef estimates here are closer to what I see, but poultry is still not dialed in.
One thing I've noticed is when my IT breast probe measures 165 (turkey/chicken), it still seems under cooked to me - with red blood? near the bones. I smoked 2 turkeys on Thursday, one intact and one spatchcocked, and both needed to be finished in the oven; even after the IT breast of the spatchcocked bird read 168, 165 in the intact. I gave one carcass/extra meat to a friend and yesterday removed the excess meat from the spatchcocked bird to make soup. The meat at the larger bones was mushy. I have no idea what that means, but I will cook to a more cooked bird in the future. I wet brined for a nearly a week and poked holes in the skin. The spatchcocked turkey skin got beat up in that process and was mostly no longer clinging prior to cooking.
My friends/family do love the experimenting!!