Year over Year comparison

I have a data model and I am trying to compare previous year unmatched to current year (Y over Y change) based on encounter_date.

I am using the following formulas to do this:

Unmatched:=CALCULATE(COUNT([ID]),FILTER(PI_Incentives_Data_Dump,PI_Incentives_Data_Dump[Payment_Amount]=0))

Unmatched Last Year:=CALCULATE([Unmatched],SAMEPERIODLASTYEAR(PI_Incentives_Data_Dump[Encounter_Date]))

Year Over Year Change:=[Unmatched]-[Unmatched Last Year]

The above works as long as I pull the encounter_date into the pivot however when I pull in the encounter_date_year (=YEAR([Encounter_Date])) it no longer works.

Any help is greatly appreciated...

Thanks