And that's just bottlers. Fountain soda is also diluted from concentrate. So local water can affect the flavor, as can the calibration of the soda fountain. The better retailers will carbon-filter their water and check calibration regularly but the average convenience store? Varies wildly.

Random tidbit from my youth: when the Coke truck would come deliver a crate of Coke bottles to our house in Mexico, each Coke bottle had a little stick of sugarcane in it. I don't think it was like that in all places in Mexico. Street vendors would have giant unlabeled jugs of Coke, and sell it to you by pouring it into a plastic bag with a straw in it.