DP: Need expression/setup to restrict custom MAPE calculations to only past periods

Summary:

DP: Need expression/setup to restrict seeded/custom MAPE calculations to only past periods. The system is provided a pessimistic MAPE of 1 = 100% for future periods.

Content (please ensure you mask any confidential information):

Seeded MAPE calculations such as "Shipments Forecast MAPE" is calculating future periods which is incorrect. We have also created our own custom MAPE measures for lags 1-6 that are calculating future periods.

Is there a way to update the MAPE expression to offset the periods to only past(history) periods?

STEPS TAKEN TO CREATE A CUSTOM MAPE MEASURE: "CATHY: Approved Final Shipments Forecast 1 Month MAPE"

1. Create measure