how to associate one product to multiple product lines and use this info in product promotions

hi experts,

I am using Siebel 8.1.14 version we are trying to create product promotions using aggregate product lines. we have one product belonging to multiple product lines. When we are trying to add default products under  one of product lines we are not able to add it. It is not visible 

Product a belongs to pl1,pl2,pl3

when i try to add aggregates it appears only for one pl1 not for others.

Any suggestions are welcome.

thanks Santosh