You can issue or sell an item, even if there is not enough quantity on hand. An item using the LIFO or FIFO valuation method results in a negative cost tier. Print the Inventory Negative Tier Report to list tiers with negative quantities. Cost tiers with negative quantities distort the true inventory cost as new items are received at different unit costs.
To ensure that LIFO/FIFO items are correctly costed, you must adjust the negative cost tiers in one of the following ways:

Inventory Negative Tier Adjustment
On the Period End Processing menu, click Inventory Negative Tier Adjustment to automatically apply positive balance cost tiers against the negative quantity. The difference in cost between the negative and positive tiers is posted to the general ledger Inventory and Adjustment accounts.
Transaction Entry

1 On the Inventory Management Main menu, click Transaction Entry.

2 At the Transaction Type field, select Adjustments to correct negative quantities for LIFO/FIFO items. Complete the fields on the Header tab.

3 Click the Lines tab. Adjust a positive quantity against the negative cost tier (the "Overdist" tier for LIFO/FIFO items) to bring the balance of the tier to zero.

4 Adjust the negative quantity against one or more tiers with a positive balance, so the total distribution equals the positive amount applied against the negative tier.