Configurable Variant Material and Make to order Costing

Dears

WE are in make-to-order variant configurable material scenario.

We have an input material which is a variant of configurable material. IM9001 i.e. we prefabricate frequently the required variants of this material and to place them in stock.

Hence, we run standard costing CK40n for these material and release the price.

My doubt is :

When we do the costing of the Sales Order for the Finished good, the above IM9001 which is part of the BOM is also costed.

It is seen that the Sales order Costing result of IM9001 is slightly different than the CK40N cost.

Since we have updated the Standard Cost of this material, why it should be costed again in the Sales Order ?

If that is the case which price will be taken up for GR : SO estimated cost or CK40N released cost ?

I am looking for guidance from you.