Even in places where concentrate is delivered, they add the sweetener (HFCS, sugar, fruit juice, etc depending on location and product) at the bottling plant.

Coke is about 10% by volume sugar, and the pre-mixed syrup with sweetener (like used in soda fountains) is usually prepared for a 5:1 dilution ratio in a soda fountain. The concentrate that goes to the bottling plants is basically straight phosphoric acid and caffeine with some secret 'natural flavors' that is usually diluted at more than 1:100 ratio with the sweetener.

This is a nice legend about the secret recipe. However production differs oflver the world. I.e. I'm the US the sweetener is high fructose corn syrup, while Europe uses Sycrose.