Ian, this was all from first hand experience gained by working on the C41 process and film family.
You have some of this backwards.
1. So called Kodacolor couplers have no relationship to Agfa couplers. Agfa couplers were sulfonic acid derivatives similar to soaps that were dissolved in the gelatin as sodium salts, but Kodacolor couplers, invented by Hanson and Vittum were non-polar organic compounds only soluable in organic solvents. They were dispersed as droplets in gelatin. The companies that used them included Agfa, Konishiroku, Ferrania, and Fuji. When the Kodak patents expired, or through gradual licencing agreements, all companies shifted to one form of the non-polar couplers or another. Some are dispersed directly in the gelatin, others in solvents, and others are chemically attached to the gelatin through an organic reaction. There are no "Agfa" type sulfonic acid couplers used in film today. Some polymers mixed with gelatin may, in the present day, contain sulfonic acids in the backbone of the polymer. This is not related to the Agfa work.
2. Some of my older, properly processed and stored E3 and E4 transparencies are fading. If you read discussions on the internet you will see that others say the same about many early Ektachromes.
3. I agree, but I was pointing out more that the formula was not accurate in the first place.
4. If the formulas are correct, I agree. Using HQ instead of HQ-SO3Na can cause problems. It is subtle, but the films were not designed for the higher activity of the HQ itself.
Again, I speak with practical research experience, not reading books or hypothesis. I've actually mixed these solutions myself believe it or not using the actual Kodak formulas. I have really run variations on some of the ingredients to investigate the effects of developer exhaustion, sulfite exhaustion, hydroxylamine exaustion, and alkali exhaustion. To do this, I had to run concentration series of each and observe their effects on the films involved.