Ana,
Let me outline what I think you do and what BC posts:
Finished Assembled Item X : Assembly Order 12345, for Item X Qty = 25
Components A, B, C, and D for Qty per. 1 each for the 4 components
When you post Assembly Order 12345, Qty for X will increase by 25 and the Assembly Order Qty. Components Inventory will decrease by the Qty per or 25 for A, B, C and D.
When I sell an Item X no other assembly posting is needed as the Inventory for Assembly Item X is in stock.
Hope this helps.
Thanks,
Steve