It's moot. the dimensions don't change enough during the build to make a difference. The circle circumscribing the tops of the nipples is the same before and after building, regardless of the spoke length.

Ther are a number of small variables involved anyway. For example we use the centers of the spoke holes in the calculations, but spokes are measured to the inside of the elbow, so there's 1mm. Also the spokes don't assume a straight line form hub to rim, taking a slightly longer route because of the interlace. The spoke does elongate slightly under tension. In the end all these small variables are factored into the different formulas one way or another, or maybe not at all, which may account for why different calculators may come up with slightly different answers for identical inputs.

In any case, the best practice is to pick a calculator, use a consistent way of measuring everything, and generate a spoke length. Build the wheels, and make a note of how much the spoke ends up off target (just sub flush of the nipple head) and retain that as a correction factor for all future calculations. After a few builds the results will be so predictable that you can calculate lengths and buy spokes with absolute assurance. (provide you're consistent in your methods)