According to SAP Library there is a fixed number (3) of initialization periods for determining the basic value and trend in APO Demand Planning. In R/3 you can set the number of periods needed for initalization in the material master field MPOP-PERIN. According to the documentation for Service Parts Planning it is possible to set the number of initialization periods.
We have reviewed the forecast BAdIs but did not find a relevant one, except implementing our own forecasting formula.
Is there really no way to influence the number of historical periods for initalization of trend models in APO-DP like we can do in R/3?