As usual, let's start talking from a pure business perspective ... When a forecast is defined, it is always required to define for which period the forecast is defined. In other words, if you forecast a demand of 200 pieces, for which period is this for? Usually, forecast are defined for a week or a month. So, what you are really defining is that your are forecasting a demand of 200 pieces for a given week, month or ... whatever period we would like to.
Now, what NAV is doing? We have the production forecast in the Manufacturing module where we define the forecasted demand on a given date (ie. 200 pieces for Nov 1st). But, is this forecast valid only for the date is defined for? Or, is it for a given period (month, week, ...)? Where do we define the aboved mentioned buckets which provide the forecast period?
The key here is to understand how NAV does the netting. It is true that when we define forecast is NAV we don’t have such a bucket set as well. Correct. That is the gap from the above business process. But, what NAV design states is that this above mentioned bucket is considered based on next forecast entry set in NAV. Let me explain this. If you set a forecast for the 1st of October and another one for the 10th, NAV assumes that forecast for the 1st of October is set for the period starting on Oct 1st until the next forecast entry (Oct 10th).
Thus, the forecast will be net against the existing sales orders on the period above calculated. If sales order is on a different period, it won't be netted against this forecast entry but against the relevant one.