Noylj,
I had to edit your post to bring it into compliance with the board policy on posting copyrighted materials.
Please read.
The important point to take away from the drawing is that SAAMI standardizes only the exterior dimensions necessary for finished cartridges to fit in a finished chambers made to their standard, and also to control bullet diameter range for shooting down a SAAMI spec barrel. Internal case dimensions are not addressed by the standard at all. The brass forming operations manager at Top Brass told me SAAMI leaves it entirely up to the manufacturer to determine his internal case dimensions any way he wants, so long as they accommodate SAAMI spec bullets and withstand SAAMI spec pressures.
For higher pressures some makers make brass thicker. Some do it by adding forming operations or stamping the headstamp deeper into the head to further work harden the brass (which increases its tensile strength). Starline makes their +P .45 Auto cases with thicker brass than their standard brass, leaving them with about 2 grains less water capacity. But Top Brass, when they've made them, has had their standard and +P .45 Auto brass identical except for the headstamp. Starline's .357 Magnum cases are thicker than their .38 Special cases, and their .44 Magnum brass is thicker than their .44 Special brass. But none of this is regulated by SAAMI standards. It's just what makes them comfortable that the brass will perform properly and that customers will be happy with it.
If you look at the NATO STANAG drawings, those do have internal dimensions; thickness of the head, thickness of the case wall at certain locations. They also have case profiles showing hardness test point locations and values. However, all these elements are "suggested" and not mandatory. (Note that primer pocket drawings are separate from case drawing in order to accommodate different primer types and sizes. Boxer and Berdan primers, in particular, require very different primer pockets.)
The bottom line: whether your .38 Special and .38 Special +P cases have different internal capacities or not can vary by manufacturer. There is no governing standard for this. If you separate your cases by brand, a scale will quickly tell you whether that brand's average .38 Special +P case is any heavier than the standard pressure .38 Special +P case or not. That's pretty much the only way to tell. With Bullseye and other fast powders, figure that for each 1.1 to 1.2 grains greater case weight, you should use about 0.1 grains less powder to keep pressure constant.