Even going back to the ‘70s there have been subtle differences in taste in Coca-Cola when it comes from different bottlers, and even different sizes and typres of containers. The Coke in a 2 liter bottle is slightly sweeter than the Coke in a 20 oz. bottle or 12 oz. can.
If you can get it in your area, pick up a glass bottle of Mexican Coke for a baseline. It costs more, but it tastes more like Coke used to taste.
Will try to find that.
When I was stationed at Mtn. Home AFB in Mtn. Home, ID, there was a coke machine in our shop that dispensed 10 oz bottles of Coke. We got a mixture of Coke bottled at Boise and at Twin Falls. I drank so much of that Coke that I could tell by taste alone which bottler it came from.
My mother-in-law buys the canned diet cokes and they are just flat out nasty. They taste like they are watered down to near no flavor compared to the fountain diet cokes. I can’t stomach drinking them. I don’t buy coke products and in general will drink water but if I am inclined to drink a diet soda, Diet Dr. Pepper or Diet Mt. Dew are my go to drinks.