The local power company sells "Green Power" but, as best as I can find out, they just shove the "Green Power" into the lines and everybody gets some of it. The people who pay the inflated price don't actually get "Green Power"--false advertising and a bait-and-switch.
Do you expect them to track the individual electrons or something? This is exactly how a system like this should work.
Users purchase x kWh of 'green' energy, so the company produces x kWh and puts it on the grid. Sure "everybody gets that energy", but it was funded by and produced for those subscribing to the 'green' power service.
It's about producing power the way a customer wants, not tracking individual joules as they float through wires. That would be madness of the highest order.