"What about the Colt .41 caliber Army Special (same as the .38 Official Police only .41 caliber) and that came before the .41 magnum"
That was in .41 Long Colt, a round that originally loaded had a .41 caliber bullet. However, it used what was known as a heeled bullet, which looks like a mushroom, with a larger "cap" and smaller "stem."
The cap is the same diameter as the outside of the case, which in the .41 LC was roughly .41 caliber. The stem, though, was .38 caliber. When the heeled bullet fell out of favor, the .41 Long Colt was loaded with bullets that were a consistent .38 caliber (no more cap, all stem). To make sure that the bullet engaged the rifling, it had a large hollow skirt that expanded when fired.
The .41 Magnum, on the other hand, used a bullet that was, from the beginning, .41 caliber, so the case is much larger around than the .41 Long Colt.