I thought it was simply a case of each organisation selling stars just makes up their own list and records your name against that, there's absolutely no link to any central organisation. I remember reading disclaimers from a few organisations doing it and they fully admit this is the case.
I've had people contact me through my website asking if I can take a photo of their star for them, I just say all it takes is $$$
They're usually happy to pay but so far none of the enquiries have been for a star that is visible at the current time - it's either a northern hemisphere star or it's only above the horizon during daytime at that time of year. I think their interest fades when they realise it can't be seen at night right then and there.
Roger.