How do I add multiple lot numbers to a single part using advanced inventory?

Welcome and thanks for posting your concern here in the Community, @LindsayB1. 

You can add multiple lot numbers to one item. I'll show you how: 

1. Go to Inventory, then select Adjust Quantity/Value on Hand.
2. Select the Adjustment Type drop-down, then select Lot Number.
3. Select the Adjustment Date.
4. In the Item field, enter the item name, or select the small arrow icon and select it from the item list.
5. Enter the lot number in the Lot Number field.
6. In the New Count column, enter the number of items in that lot. To assign a different lot number to more of the same item, or to assign a different lot number to a different item, repeat steps 4 and 5 as needed.
7. When finished, select Save & Close.

Once done, confirm the accuracy of your entries by running the Serial/Lot Numbers in the Inventory report.

You can check out this article for further insights about using serial or lot numbers in Quickbooks. 

Keep in touch if you have additional concerns. I'd be happy to get back and help again.