"The Stones" mentioned by the Black Lich, I think, were the
Prophesy Stones that foretold the forming of the Order/Chaos Guards. This was an event that I mostly missed, but there were some sort of stones placed around Sosaria with riddles that had to be solved. I think the letters were jumbled, or something like that, and it was the Mage Towers ( a collective effort from all the shards' Mage Towers), who solved it all (and it was pretty complicated as I recall). The 3-4-1-5 was used to put the stones in an order, somehow, if I remember right. So that reference wasn't really part of the original intention for the numbers in Covetous, although it still could be a clue. From time to time I get an idea to check out, but as you might expect, no luck.
I've searched the internet, not just this time but many times in recent years, but I have yet to find anything about that event besides the solved riddle, linked above. My memory may be wrong about this part of it, and that's why I've searched along with other questions about "it all".
There's also been several times that EMs and player events have used those numbers. But again, those incidents don't really have anything to do with the original meaning of them.
It's almost certainly one of those things that never were finished. But I still get that ol' "what if" feeling from time to time.
I've spent a lot of time on this stuff. I love a good mystery. The only thing I can think of right now that might be related to these numbers are these "fittings" in Dungeon Hythloth (pictured below).
These were added years ago, but well after UO was released. What they are for I have no idea. There are 5 fittings, so number wise they could possibly be related. Does anyone know what these are for? A quest? Ever find anything that "works" them?
Edit. I should correct myself. There are a LOT of things that could be related to the numbers. But those fittings are the only thing that I don't know about and haven't been able to check out to some degree.