Ok, that clears things up.
The challenge about not having real time info would be:
1. Inventory quantity status (either raw mat, semi finish goods [SFG], or finish goods).
2. Costing.
What can be done here would maybe be create a few warehouses:
A. Bottle cap warehouse (SFG). * Note that the bottle cap has its own BOM.
B. Bottle warehouse (FG). *Note that the bottle cap is part of the bottle BOM.
Since the Bottle BOM cannot in theory run without having updated quantities for bottle cap (SFG), you can circumvent this by setting the bottle cap BOM to be backflush.
(For more info and some reading on 'backflush', please see here --> Issue Method)
Else, SAP B1 will always see insufficient quantity in either BOM due to the fact the inventory details is not real time.