If the item did not have a standard cost assigned when shipped, at what value did the item go into inventory ??  At $0???
 
When an item ships, the entry is to relieve inventory at a value (whether standard cost, average cost, LIFO or FIFO)  and this SAME VALUE becomes the COGS.
 
If you adjust the COGS after the fact, you need to adjust inventory and this will create an inventory variation unless you also correct the original entry to finished production or if purchased, the receipt of the material.