The 'unit cost' on the Item Valuation report is any of the Average Cost, Most Recent Cost, or whatever you select for the 4 available costs to print as columns for the report. Then Total Cost is determined by multiplying the unit cost and the quantity on hand.

If you backdate the Item Valuation report, even by one day, then the 'unit cost' is calculated by taking the Total Cost as of that day and dividing by the quantity on hand as of that day (both calculated by taking the values as of today and adding or subtracting Historical Transactions for that item dated later than the report date). This is because Adagio Inventory does not store every Unit Cost for every date each time it changes. Only the current and next recent cost value.

If you ever post adjustments to Inventory, make a backup of the data prior to doing this. As Steve mentioned, there may be a very good reason to post a Cost-only adjustment, but the question arises as to how this happens (such as a previous incorrect Adjustment or Physical Inventory transaction requiring reversal).

What was the answer to Andrew's question - what is the Costing Method of the item? If shipments use a different cost than the Average Cost, then either your item doesn't use the Average Costing method, or the average cost at the time of the shipment was different than it is now - perhaps due to changing the total cost of the item and not the quantity, or changing the qty and cost and at a different ration than the average cost.