Aloha,
Universal Rule proposed by NGH in 1903 for NYYC, refined then adopted after the 1903 America's Cup. Not really in effect until 1905 or so, as we see different citations of "first NGH boat designed for the Universal rule."
Yes different designers took a crack at boats for the S Class, as they did with other classes (P, R and J come to mind), one drawing even shows the 828 class S Boat with a "17 rating" which suggests they were raced against other classes on handicap; however the Herreshoff S Boat allowed close racing (one design as it were) and could be ordered in quantity as they did for the various fleets discussed. By the 20's the Haffenraffers were running the business so chances are they promoted Fleet pricing.
As far as the print date of the plans--most sheets contain what I would call a blue print verification stamp in the lower right corner, with handwritten initials etc. from Herreshoff Manufacturing, Co. Possible added later, but there are details like "drawer #" that make me think they were done as dated ie. 1919 through 1920.
The earliest dated drawing is Nov. 1919, Rudder drawing is Dec. 24, 1919, a drawing for the water tight cockpit is Jan, 14, 1920, Peconic Bay keel drawing Sept. 20, 1920, Shear strake Nov. 29, 1919, Rig Drawings are late November through early December but has one dated April 16, 1919 which also has listed "Boom socket for 702" so perhaps this was from another knockabout type boat. The latest date is a complete drawing of the vessel and rig dated Nov. 1, 1924.
Perhaps drawings were penned out when orders for more vessels came in so that they could be reproduced more efficiently and consistently.
Charles