I believe you are asking for a new field to show stock available based on 'what you can make'. 

There is a module that extends Odoo to do this.  It allows to you add a stock quantity you can 'promise'.  Odoo shows by default the QTY ON HAND and QTY FORECASTED.  If you want to know what you can promise a Customer you can ship today, you need a new number, removing the projected incoming stock quantity from QTY_FORECASTED, so that you can just see QTY ON HAND minus QTY RESERVED for orders.  In a similar way, you can configure quantity you can 'promise' based on 'what you can make'.

https://www.odoo.com/apps/modules/9.0/stock_available/

This module proposes several options to compute the quantity available to promise for each product. This quantity is based on the projected stock and, depending on the configuration, it can account for various data such as sales quotations or immediate production capacity.

Hello,

It's not correct, a component would always show it's actual physical stock in hand irrespective of what pack it's assigned.

Also a component can be used in more than one pack or Bill of Materials, at the same time, one BoM can always have many components with different quantities.

Regards.