Filemaker Pro Script problem

Trying to fix a script which will allow me to combine or merge two inventory files together to provide one consolidated Master file. Both files contain the same matching database fields. The files contain matching data entries containing different inventory values as well as unique data entries with inventory values. Where there are matches then the inventory values need to be shown individually together with a total field of the two values. As you can see we have pulled all this together using the master 'wholesale' file which pulls in data from the two individual stock files via an interim SKU Generator file which first identifies and deletes any duplicates. The only problem we have is that the stock values are not importing correctly - for example taking SKU 450367105 the individual values on the UK file are S-3 L-1 XL-3 and on DE XL-1 but the total combined stock on the _Wholesale file reads S-2 L-2 XL-2. We can't seem to fix this.