Planning in manufacturing involving item variants

Japnav

Dear all,

I need advice here. I have this case with regards to planning in manufacturing involving item variants.

NAV 2009 - Module: Manufacturing-> Planning worksheet

Background:
Raw material - Item A Variant 1, stock on hand: 20
Raw Material - Item A Variant 2, stock on hand: 30
When we look at quantity balance of item A in item card, there is 50. Item A variant 1 and variant 2 can be mixed to be used. The difference is they are from different manufacturer. The cost of these variants can be different too. Physically, when they are put together, we can not tell the difference.

FG X is a finished good.
for 1 of FG X, it uses 1 unit of item A.

There is a need to manufacture 70 of FG X. When we run planning worksheet, NAV suggests to buy item A 70. I wonder why it does not take into considerations those with variants? It should suggest to buy item A 20.

Do I misunderstand the concept of variants? do I use substitution? but for substitution, since it is different item code, NAV will not suggest to planner that there is substitute when we run planning worksheet.

Please advise on my understanding and if you have similar case, please kindly share how we should handle this.

thank you

Jap