The stock valuation from the Audit System areas window, found by pressing Ctrl + A only reports on fields which can be edited on the stock valuation screen itself; namely the Notional Sell Price and Valuation Code. However, these fields are hidden for most users so there is unlikely to be anything in the audit.
The standard cost history for a part can be viewed by completing the following steps:
Select stock
Select stocked parts menu
Select stocked part maintenance
Hit enter and select relevant part
Press F6 to launch the stock summary window.
Click into the Standard Cost field and press F5
Click History to see the standard cost history of this part