I don't think I quite caught the gist, but I made an attempt.It sounds to me like you are blending your two datasources?
It is feasible to join them?
If so, you can use a level of detail calculation to fix the historical counts so that they won't be affected by any filters.
Please see workbook v10.3 attached in the Forum Thread:
Also attached is the datasource I used. If I have missed the boat, please adjust the datasource
and workbook to more closely match yours.