Difficulty counting differences between old and new products

Hi, for the sake of this question I have a set of old products which are being migrated to new products. Each product has a set of attributes which I want to compare so that I know how many differences there are for each migration mapping.

Here is some data. The mapping table looks like this:

The Product table looks like this:

I want to know the number of differences across all Attribute columns for the chosen 'Old' and 'New' products. Also, the number of Attribute columns may change.

So far I have separated the attribute fields into a separate table in Power BI so that the model looks like:

In my report I want to select a mapping from product X to product Y and show:

• A list of attributes and their values for both products
• Whether the attribute is the same for both products
• A count of how many differences there are between products

So the report looks something like below, except that the count of differences is not correct.

I have 4 measures:

1. Old Product Attribute Value = SELECTEDVALUE('Product Attributes'[Value])
2. New Product Attribute Value = CALCULATE(SELECTEDVALUE('Product Attributes'[Value]),USERELATIONSHIP(Mappings[New Product ID],Products[Product ID]))
3. Attribute Match = IF([New Product Attribute Value] = [Old Product Attribute Value], TRUE())
4. Count Differences = COUNTROWS(FILTER('Product Attributes',[Attribute Match] <> TRUE()))

Firstly, is it the best approach to seperate the attributes into another table or is there a better way to count differences across columns without unpivoting the product table?

Secondly, if splitting is a resonable approach then why is the 'Count Differences' measure not producing the value I expect to see?

Thanks in advance!