Thanks for detailed explanation.
Could you please shed some light on what steps could be taken to improve if car hasn't been run with proper fuel resulting in "bad fuel mileage (slow burn), more deposit (slow burn), damaged cat (slow burn) and oil contamination (slow burn)".
Are products like "Fuel Injector Cleaner" (ref: link) and such of any value or just marketing stunts like Octane Boosters?