Some Extracted Ariba Invoice Line Item Data via Procurement API Does Not Match with Order Line Item

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In the Invoice Line Item table extracted from Ariba via the Procurement API, there are records created from purchase orders where the purchase order line item number does not match the invoice line item number. The ratio of unmatched records is 20.89%, with 80,373 out of 384,822 records affected.

See below: 

Bold columns are foreign keys that join the Invoice Line Item Table to the Purchase Order Line Item Table in SQL. In the yellow cell, it returns "2" as an Order line item number(OrderLineItem_NumberInCollection), but the original purchase order line item number was "1". There is no other record that has "1" for the purchase order line item number. The original purchase order line item number "1" is not cancelled or rejected, although its price was changed by a supplier. I need to know when an overwrite of the original purchase order line item number in the Invoice Line Item Table occurs.