You are close on the calories, but you are right that I was wrong.
It should say 16 servings of dextrose, which will change the formula a little bit.
Dextrose is 4 carbs, 15 cal, x 16 servings = 240 cal
Milk is 3 x 80 cal = 240 cal
So it is 480+ if I add the additional dextrose. I will probably go pick up some maltodextrin in order to raise the carb count and not have to drink sugar.
The dextrose is utilized just for this reason:
“In addition to reducing fatigue, use of carbohydrates during exercise will speed the rate of recovery after exercise by inhibiting proteolysis, especially if protein intake is adequate”