Subject: World championship rules 1974
On your Fischer forfeits to Karpov page [link given above], you wrote, "The same rules governing World Championship matches had been in place since the 1949 FIDE Congress in Paris. They were confirmed at the 1974 Congress in Nice."
In Bozidar Kazic's article "Anatoly Karpov The New World Champion" in Chess Informant 19, he writes that "In September 1971, the FIDE Congress in Vancouver decided that ... the world title in 1975 will be played for 6 won games draws not counting." In 1972, Euwe reportedly tabled a proposal for a match of 30 games. At Helsinki, Fischer sent his 10 wins and 9-9 plan, and a commission was created to draw up rules. At Nice, Kazic has them adopting a match of 36 games where one could win ahead of schedule by scoring 10 wins.
Indeeed, the referenced Informant has two-and-a-half pages titled 'An Outline of the Dispute Over the Unplayed Match' with a summary of FIDE actions between 1971 and 1975. While looking a bit more into the background of the 1975 match, I discovered the following table in a 1974 article titled 'The Historical Background' by Frank Skoff, President, USCF.
Chess Life & Review, October 1974, p.652
Although it might contain its own errors, it's a good summary of pre-WWII top-level matches and shows that Fischer's demands were not as outrageous as many of his critics declared.