You'd think a Short Barrel round would be rated from a short barreled gun, inherently lower in velocity. Likewise, a 38 Spl +p would not likely be rated from a short barrel. The Speer book shows that to be the case, using either a S&W Model 19, 6" or a Model 19, 2.5".
The median velocity for suggested Short Barrel loads using Unique is your 990 fps. However, 5 out of 7 powders listed are higher. The median for AA #9 is 1230 fps. I think then that your characterizing Short Barrel as a 38 +p load is straining to be cynical about the round and those who use it. In reality it is a very well suited round for light weight and short barrel 357s, yet is still within the range of being a bona fide .357 Magnum.