PowerBI - subtract two columns from different tables

Hi,

I need your help with the following problem. I have two different but similar tables from which I want to subtract two columns (Cost). For confidentiality reasons, I cannot provide the data but I will give a simple example:

Table A (imagine that I have multiple Product Clusters, Products, Years, etc. - this is a simplified view):

Table B:

Both come from the same Excel file and tab, with the only difference being the file version (version controlled on SharePoint). Many users can edit this file and I need to provide a quarterly review and capture the Delta.

Note that while transforming my data, I am filtering the data creating a new column to split the Sum from Cont. entries (Add Conditional Column filtering Sum).

What I have done is add an Index column to each table, create a 1-1 relationship and it worked. However, when I took another file version (same structure, same items on the same lines) it messed up the Indexing resulting in a mess.

I understand that the Indexing idea was not perfect as it cannot handle changes in line items - which can happen.

Is there anything else I can try?

Thanks,

George