Understanding: The quantities required, finished and remaining at the operation and in total for the Shop Order
The shop order may require 1,000 pieces but only 950 are reported as finished in total for the shop order. The quantity required is what is planned on the SO and it may be a higher number than what is finished, factoring in that there can be scrap. If a 1,000 pieces are required to be produced, and there is always is scrap of 10 pieces, then plan for scheduling a quantity of 1,010.
The quantity finished for the end item is what is reported in the inventory application with a production order receipt transaction. At the operation level, if the quantity is reported at the operation, there will be a value in the PCS Complete field on the operation detail screen showing the pieces completed through that operation.
If you want to get a handle on the difference between the required quantity and the finished quantity, you may want to look into reporting quantities at the operation level as well as examining how scrap is controlled and reported.