In the FIFO Cost Lot Tracking report, why are some bills associated with invoices created before the bill?

In the FIFO Cost Lot Tracking report, some bills will be associated with invoices created before the bill date because Zoho Books follows the First In First Out (FIFO) format. Let’s consider a scenario where you create an invoice for an item with zero stock. Once the invoice is created, the item’s stock will be negative. Now, when you create a bill, it will reset the negative stock of the item. As such the bill will be associated with the previously created invoice.