Special R contain sweeteners. Special R tastes like crap. Regluar Ribena doesn't have any added sugar, it's natural fructose and stuff from the fruit that's used to make it. I have no concern over calorie counts. It's expensive enough that I only buy it when it's on offer which is every few months.
Brushing after a swig of Coke is one of the worst times someone could brush. Coke is essentially acid. (carbonated anything, is acid) So what someone would be doing is brushing and rubbing acid into their teeth. The best time to drink carbonated drinks if one must, is to do it at meal times, the bodies natural saliva etc helps to protect the mouth.
So what happens when you eat dinner and don't brush until 12pm? The plaque produce lots of acid in that time. By your reasoning you're then 'brushing the acid into your teeth.' That doesn't seem to do the four or five billion people who brush their teeth every night much harm.