First, in order to compute state functions we often devise idealized paths to get from initial to final states, since we know that the value of a state function at each extreme is independent of path. The path we pick is a reversible one usually, and where the intensive variables describing the system can be related functionally in some simple way that allows us to compute the difference in the state functions, using for instance the ideal gas law. These idealized paths have nothing to do with the actual course of the experiment. Still, as long as the initial and final points in the calculation and experiment match, the computation should (within the approximations of the model) be an accurate descriptor of what happened experimentally to the state functions.
A second and perhaps more important issue is that, as you may note ocassionally in textbooks on experimental pchem, variations in $\Delta S$ or $\Delta H$ with T or P are often ignored, assuming we are working over a limited range of T and P. That assumes (in the case of variable T) that the heat capacity of the substance can be ignored.
However it is not generally good practice to ignore heat capacities over an extended temperature range, and computing $\Delta H$ at a new T is not difficult if you have available heat capacity, which can be assumed in your T range, and enthalpy data at a single point in that range.