Absolute Ring Event

I don't see that working, but it is worth a try. I mean, since they have all been transformed into tradable, what is to stop you from transferring the ring to another character, waiting an hour, getting the potion, then using it on that ring (and repeating on multiple characters until it becomes max level)

It's because it's tradable that Gaga won't let you upgrade the ring. Even if you were to upgrade the ring on another character, it wouldn't count towards your checklist, which is what ultimately matters toward your upgrade total.