Check for value or write new line

I have a spreadsheet that I am using to keep track of my inventory.

The sheet has 4 tabs:
Stock - shows current inventory levels
Received - all inventory that has been added to inventory
Issue - all inventory that has been removed from inventory
ItemList - Lookup page for product names/descriptions.

I enter new inventory into this spreadsheet in the blue columns on the Received tab.
The new entered line is copied over to the Stock tab by copying the Received cells one by one...and the summing them in E.

The hope was that there would never be duplicate items entered, but I was wrong.
Rows 23 and 24 are duplicates because the same Item No, Pkg, and Lot exist more than one time.

What I would like to do is have the sheet look at the concatenate value in the received tab and compare it to the concatenate column on the stock tab.
If a match is found, add the value from the received tab to the corresponding cell in the received Qty column on the stock tab.
If no match is found, add the information from the received line to the next available line in the stock tab as a new item.

Hopefully that makes at least a little sense.

Thanks,
Anthony

Originally Posted by excelisfun009

Try to simplify your original question in few arguments

I would like to be able to have entries on the Received tab checked against current entries on the Stock tab.
Column A on the Received tab exists on the Stock tab, add the Qty entered to the existing inventory on the stock tab.
If column A on the Received tab does not exist on the Stock tab, add that row to the Stock tab as new inventory.

I really wish I knew how to explain this better...hopefully it makes sense.

Thanks,
Anthony