Well the Sales Order has to be shipped before there is an Outbound Entry in the Item Ledger, which will be linked to certain inventory. However, that Sales Order will be deleted once it has been invoiced.
For the accurate cost you can use the Item Ledger Entries / Value Ledger Entries for the Sale after you have invoiced the Purchase Order receipt used in the sale, and after you have run Adjust Cost. The correct values will be in the ledgers.