These are ignored by the system since in most cases they are not needed.
Usually, these are consistent with your overall demand trends, so there is no need to explicitly take them into account, since the forecast will automatically cover the expected sale. This will be the "Forecasted Demand" calculated field.
However, if you have future sales orders that are extra, or inconsistent with the sales history you can set the overridden demand for an item. In the demand analysis set the "Set Manually" amounts for each future month. For manufactured products, this will then update the forecast for each of their components. You can also do this in bulk via CSV, under Load Data -> Show bulk forecast upload.
Taking into account future dated sales orders is not something the system can do automatically unfortunately, since it's always unclear whether a future sale order is in addition to the predicted demand, or whether it's just part of the business-as-usual demand and already taken into account from the sales-history-based forecast.
So that's why the system is designed with this extra option to manually set the demand, so that it's clear for both you and when the future calculations are made.