@bfpierce999 

It sounds like the difference is due to the average cost.  Are these books that have been reordered over many years?  As the cost changes over time, QB recalculates the average cost of the item but apparently does not make inventory adjustments based on the average cost.  Maybe you have seen this step on doing a value adjustment when adjusting your inventory in QB for Mac:

If you need to, edit the value of the inventory after adjusting the quantity. QuickBooks will recalculate the value based on average cost. When you edit a value, you change the average cost of the items in stock. To edit the value, select the Value Adjustment checkbox. In the New Value column, enter the value for each inventory item whose value you want to change

The other option is that if you know your quantities are accurate and we are talking an immaterial dollar amount ($600, right?), you can make a journal entry to adjust this.  If you need to reduce inventory in QB, debit cost of goods sold, credit inventory.  If you need to decrease inventory in QB, debit cost of goods sold, credit inventory.