OurOrderNumber field is not populating on Custom Exports

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Hello Again!

It appears that our column for order number is not appearing on the export. I have tried an export in both the OE and AR modules, and it does not seem to be saved. 

Where does this information live? 

Specifically I am trying to get the order number of an order, after it has been invoiced. I would like to match the order numbers against the invoice number for some third party accounting projects. 

Thanks!

Devin