Problem with fusing

Honestly, I am not convinced that there is a unique ID at all. It could be something simpler such as a Time Stamp. Time stamps are very precise and don't need to be sequential. If an item has a unique ID, the growth of that ID number in a game like this would be astounding. Every item would add 1 to the ID number and the count would have to be maintained per server for all items simultaneously. That's a lot of work for the database engine. A simple Time Stamp on the item would make it mostly unique. Thus, a Duped item would have an identical time stamp as another duped item. It would then be likely to be a questionable procedure to delete items based on a Time Stamp since there can be any number of legitimate items that share the time stamp. It is particularly true when there may be certain events in the game that alter the time stamp. MTS trade may do that since it the item can change servers.

(I am using Time Stamp as an example here and not as a fact. None of us knows exactly what the item record contains and thus all of it is speculation.)

Generating unique ID's is a pretty basic function in Oracle, which provides a "sequence" entity that auto-increments every time it is fetched. I don't know whether MSSQL has a similar entity, but it's not that hard to implement one yourself.
Using time-stamps, or any non-unique "item ID" completely defeats the purpose of using the item ID to know what is in your inventory. The reason dupes don't break the game is that all items with the same ID are similar or even identical (e.g., all items with ID 123123123 are a VIP Bow). If you use timestamps or the like, you'll get weird situations like trying to equip a stack of potions.