I'm not familiar with IIG matrix but you can set up alias records for an item in Item Maintenance and that could maintain the link between a UPC code and your internal item code. 

Alternatively, if you will only ever have one UPC code per internal item, you could set up a UDF in CI_Item to hold the UPC code, going this route would eliminate the need to link in the IM_AliasItem table.

I see your point but it will not work for us because the item acts as a parent item, it can't have a UPC code, the children (lot serial numbers) contain the UPC code.  So within an item IIG gives us the ability to add different color size combinations under one item code.  Our catalog of item codes would be outrageous if we didn't use the enhancement.

If the inventory is Lot valuation, look in IM_ItemCost, which is where that data is stored (Cost Detail tab of Item Maintenance).

Yes, inventory is in this tab, but I'd have to back track to tie the UPC to the Lot No. correct?

Sorry... I have never worked with that enhancement, so I don't know how it works.  I thought the UPC might be embedded in the Lot# field.  If there is a linking table, I have no insights to provide.

One trick for finding the table where certain data is stored: make a change, then go to the MAS_###\??### folder and look at the date modified on the M4T files.  (Only works for Standard / Advanced, not Premium).