Which global parameter can't initialize the forecast input key figure when historical data is missing?

The MAX_DIM_MEMBERS parameter is related to the limitation on the number of dimension members that can be processed during calculations for forecasting. This parameter specifies the maximum number of members that can be included in one calculation. When it comes to initializing the forecast input key figure, its role is not directly tied to handling scenarios where historical data is missing. Instead, it acts more as a threshold for computational efficiency rather than a means to address the situation where data may not exist.

In contrast, the other parameters have specific functionalities concerning how the forecasting process can adapt to missing historical data. The FORECAST_ALLOW parameter allows for generating forecasts even when historical data is incomplete, so it's designed to handle those gaps. The MTHMISSIONS and DYNAMIC_FORECAST parameters also possess functionalities that support forecasting with variations and calibrating predictions based on available data inputs.

Thus, while MAX_DIM_MEMBERS serves a purpose in managing dimensions, it does not provide the capability to initialize forecast inputs when historical data is absent, making it the correct choice in this context.