For the last time:
If Victor bought that ring for Yuuri ahead of time then the anime would have shown us. And even if they wouldn’t have shown it, if that’s what they wanted us to think, they would have made it explicitly clear. Especially in the episode that was narrated by Victor.
What interest does the anime have in hiding the information that Victor bought the ring earlier?
Which is probably enough reason to believe that it didn’t happen.
Listen, I know it’s a really sweet idea and I know that we’d all like that to be true, but there are limits to wishful thinking.
I keep seeing people speaking of the headcanon (because that’s what it should be called) that Victor bought the ring ahead of time as though it’s a fact and I think it’s very confusing and even misleading to a part of the fandom.
And listen, if you want to believe that’s what happened, that’s cool, but at least acknowledge the fact that you’re talking about a theory or a headcanon like I mentioned above, and don’t act like that’s what canonically happened because if that’s what it really were then it would be clear to everyone and we wouldn’t even have to have this argument.
(Especially that there is much more proof for Yuuri buying both rings/Yuuri and Victor buying the rings in the same store at the same time than of Victor buying one beforehand.)