How does NetSuite natively track which line items from a sales order have been exported to the company's pick / pack / ship platform? If one of our line items is on backorder, it doesn't export to the pick pack ship system because there's zero inventory. So how does NetSuite know that that item still needs to be exported to the pick pack ship system after that item gets more inventory and comes off backorder?

Sounds like it's based on committed quantities.

It based on accounting preference where you can fulfill what you’ve in hand if you set accounting preference ignore commitments than you’ll see non committed lines on the fulfillment too.