Don't be. The chart's wrong. Maybe because The Possible Shop doesn't stock the Treso 11-50-01. The 11-50-13 fits Thompson/Center rifles and is thus a popular size; the 11-50-01 fits some shotguns and the large frame Colt and Uberti revolvers which are less popular in overall numbers.
As I said the difference is 0.10" in overall length. Here's the specs:
11-50-01: 1/4x28 thread, 0.635" long
11-50-13: 1/4x28 thread, 0.538" long
There's a third 1/4x28 thread Treso nipple, the 11-50-11, which is even shorter, 0.494" long.
In a properly timed Colt revolver the hammer will hit the frame before it hits the nipple, but it will hit the cap. In such a revolver the 11-50-13 nipple will not work. However, our Italian revolvers are rarely timed to such precision, so the hammer will usually strike the nipple before the frame if no cap is present. It's most likely that your revolver will not care whether the 11-50-01 or the 11-50-13 is installed, but the former is the proper one as it better matches the OEM nipple length.