As already indicated a Forecast needs to be refreshed before it is available for review. This can be done per individual Contract Forecast screen.
GENERATE FORECAST LINES - BULK:
A utility that generates / refreshes these Forecasts for a specified range.
Overwrite Existing Forecasts
This allows you to overwrite an existing forecast for the specified Period by selecting the check box.
If you did not select the check box, it will not overwrite the existing forecast, and any forecast created will remain the same, However any contract that did not have a Forecast created for that Period would refresh.