When you have these long term predictions which you plan on keeping track of, it is helpful, if possible, to create multiple models to apply to each forecast so that in the retrospective one can determine which, if any of the models, was more successful than the others.
So perhaps you have a prediction about how many volunteers will be required for a particular initiative to save x lives 10 years out. If you keep three separate forecasting reports which are explicit about their reasoning, then the iterative improvement process can happen a bit more quickly.
When you have these long term predictions which you plan on keeping track of, it is helpful, if possible, to create multiple models to apply to each forecast so that in the retrospective one can determine which, if any of the models, was more successful than the others.
So perhaps you have a prediction about how many volunteers will be required for a particular initiative to save x lives 10 years out. If you keep three separate forecasting reports which are explicit about their reasoning, then the iterative improvement process can happen a bit more quickly.