Selected Answer
You have a product that has no regular demand. Therefore whatever forecast you make is a guess. You can apply some lipstick to it but it's still only a guess. Here is the lipstick.
- You might weigh last year's demand with whatever percentage you like, or the average of the past 5 years, or both last year's and an average of past years, or allocate different weights to numbers from previous years (the younger, the higher).
- I would not recommend to allocate a minor weight to the forecast for political reasons. Somebody put some thought into that number (hopefully). To plan for 1288 pcs in your example (weighting 80:20) has no logical foundation.
The alternative to guessing is to try and guess intelligently. That isn't much of an improvement but that is what people do.
- The forecast may (should) consider offers submitted to potential customers. Therefore it is useful to look at the percentage of offers which resulted in orders in the past and, perhaps, the delay with which this occurs (to possibly push some of the quantities into the following planning period). Then look at the current economic outlook in your branch of business and try to extract some logic from it that might affect the realisation rate.
- Look at the relationship between past forecasts and actual use.
Putting the two above branches of thought together, some predictions about future development are possible based on the trajectory of a past performance curve. It would be moot to discuss the merits of that here because your product's past performance curve doesn't have a trajectory. There is nothing to be learned about the past that could be applied to the future, even if that were otherwise commendable. Therefore your only logical course of action is to look at the method of how the projection was made and apply other trajectories to the resulting numbers, such as whether your company and/or its market is growing, and try to find a measure of performance of the sales team.