Using SUMIF to gather the info that doesn't match

Originally Posted by mistrmoto

but I was hoping to be able to use something similar to a sumif.

Why?
That's just going to create extra unnecessary calculations for Excel to do = slower performance.

Excel has already done all the required work with the sumifs finding the ones that DO match.
No need to do more work to 'find' the ones that don't match.
Simple logic says what remains after the sum of values that DO match, is the values that don't match.