IFMU,
The S-1 was Igor's first machine, and it didn't make it over the trees. The S-2 did, and so on!
The S numbers were used for big proposal efforts as well, so not every S number flew.
The only Sikorsky machine without an S number was Comanche, which was a Boeing collaboration.
I flew the ABC, it had regular controls, lots of them! 225 knots was a scream, frankly!