UK Duplicate entry of Cost of Sales

[Roelf_zelf]

I can't figure out the correct booking for the following problem.

My cost-price of a manufactured item is based on the purchase price of the item, + the cost of some stuff added to the product + labour cost to produce said item + a bit of overhead, etc.

When I buy the stuff that has to be added to the product, I booked it directly in CoS.
COS NON INVENTORY
-> A/P
Theoretically all that is booked here, should be invoiced out eventually.

Also the labour cost are booked here:
COS PRODUCTION WAGES
-> BANK

The main raw materials are booked in inventory.
INV HALF PRODUCTS
-> A/P

When invoicing the manufactured item this is the entry.
A/R
COS FINISHED PRODUCT
-> INV FINISHED PRODUCT
-> SALES
-> VAT

Now the CoS Finished product is the cost price with all the added items, which were already booked in CoS Non-inventory.

I'm trying to make a monthly correction on this:
INV FINISHED PRODUCTS
-> COS NON INVENTORY
-> COS PRODUCTION WAGES

That looks very sloppy, and I'm not even sure this is correct. There must be a better way.

Can anyone help?