Tracking UID in a database is unique for UO, due to the nature of the system.
UID's (Unique Identifier) need to transfer between shards, and you need to insure unique part of UID stay unique when the transfer of the item is done.
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Using this you can capture and track the ID, and the history of the ID as the object transitions inside the game world.
Good explanation - let's add something though. You can use the same search and identify system to build a tool that automatically deletes any other item that tries to claim an item ID already in existence. Hell, you can even make it blackhole the character with the dubious item, and auto page a GM to come investigate.....
Needs time, development and effort? Yep - apparently though, whilst spending tens or hundreds of thousands on KR was worthwhile, fixing the dupes/cheat market was and is not. Easier to flail about banning people, making various hot air speeches about commitment to cleaning up the game and having zero tolerance for cheating, and then letting things go back to the usual state for a while until the next burst of hypocrisy and another ban-fest.
I'm seriously upset about what's happening now - the EA/Mythic approach is to let a load of duped stuff remain on the servers for weeks and months, being traded on vendors or between players, accounts and shards, and only WAY too late leap in and ban people for having the stuff. Sure that gets some of the cheats - but not all, and also drags in too many other folks.
If they were really serious about this, they'd be deleting duped stuff almost instantly - and not wittering on about 'we don't want to give people warnings we are onto them', if the items are getting automatically deleted very shortly after creation, there isn't a problem with someone wasting their time making the dupe.