For B31.3 expansion stress, I typically would evaluate the total temperature difference, for example T cold = -20F, T install = 70F, T hot = 200F, Temp difference would be dT = 220 F. The way I read B31.11 piping (restrained or unrestrained) I would compare the maximum of T hot - T install or T cold - T install. So in the example above, dT would be 130F. Is this the correct interpretation of B31.11?

I don't have a copy of 31.11 in front of me but some piping codes focus on evaluating stress for each "state" of the system rather than the stress "range" between these states. Your reading would be consistent with that approach.