The implication is that Coca-Cola is not invented in any form in the US, there is no American Coke of any kind, the closest being Pepsi.
Ah, OK. So instead of OTL Coca Cola there exists something that's similar in taste and carbonated but is more like OTL Pepsi than Coca? And is called something else, let's say Pepsi because it's simple. ATL Soviet Coca Cola (called something else but let's call it this for ease of argment) is same as OTL Coca in taste.
In that case Pepsi just takes role Coca had OTL. They are not that different so that wouldn't be hard. Coca Cola is seen as Pepsi rip-off and communist attempt to copy US product, admitting it's that good even Soviets want it. But how popular it would be? As I've said, others tried to provide alternative to OTL Coca but that was because it was already popular, people wanted it but governments didn't want their people to drink decadent western drinks. If ATL Pepsi doesn't penetrate into soviet market prior to 1920s then there really is no need for ATL Coca to be developed because there is no need to counter such penetration.
And somebody saying "Hey, I've seen this drink in US and I think if we copy it, relabel it and sell it it will be a success" is't soemthing that is likely in Soviet economic system.