We are having issues with Manufacturing order back orders. 

For Example: Our Workshop is manufacturing 600 units of a components. There are multiple stages to produce each (E.g. Cutting, Machining, Hand finishing) So we start all 600 at the same time. In order to make these components available for the next stage of production, we made a partial delivery of 100. 

In this example, how should the timings be handled? I assume the timings on the first MO are the timings for all operations up until the backorder (E.g. all 600 components). In this case, the batch of 100 would be costed based on the entire MOs timings.

Is there a better way to handle MO back orders so that all the costs are split evenly across all components?

Thanks