Actually, the IOR influenced design of cruising boats well into the 1990''s. For example, Jeanneau''s ''Classic Series'' are basically IOR hulls and rigs. The real watershed for the IOR was the mid- tp late 1980''s. It is during that period when the first purpose built IMS boats appear. If you have to point at one particular boat that changed the world during that time, it would be the Farr designed Goucho. Up until then, IMS was a ''run what you brung'' sort of a rule. Bill Tripp had designed some earlier IMS boats that were very good for their day, and the J-44 was seen as a revelation, but it was Goucho that really showed the world what IMS typeform would look like and what it could do.
The CCA rule was a post WWII effort to correct the excesses of the earlier International and Universal rules. The IOR first came into use around 1970. I still have a 1969 article by Olin Stephens that introduces the IOR rule and explains how the IOR will eliminate the excesses of the CCA rule.