When I was young, my neighbor was an MD GP who had worked as a pharmacist early in his career. In those days, Coke was mixed on site by the pharmacist for the fountain, so he had the formula. Some years later he bought the ingredients to make his own, and was visited by Coca Cola to inform him of their rights and "discouraged" from ever making any drinks. Today, its probably even easier for Coke to 'patrol' using big data.

My own experience with Coke is that I drank gallons of it when I was in college in Atlanta (Coke HQ.) It was G R E A T tasting. A year after graduation I moved to Houston to consult and the taste of the coke made there was very disappointing. I stopped drinking it. Then a friend invited me to a 50s party at the Greek church. They had the 6 oz bottles for the event and I noticed the taste was GREAT again, so I got another bottle (6 oz is not enough;^) The 2nd bottle was disappointing again. I checked the bottles and found the good one was bottled in Birmingham and the bad one was from Dallas. I concluded that the water used was the reason for the obvious taste difference.
Of course, today the formula has nasty corn syrup and the taste is bad even in Atlanta.
Fortunately I lost my taste for it and now it is only a small ingredient in Long Island Iced Tea.
That tastes GREAT ;^)