Source and Usage of "Availability" field at BPA Line Level

Summary:

BPA Line has a field to store "Availability." I don't see this field on the FBDI import, and I don't see what table and value this is drawn from in the system.

Availability sure sounds like a good spot to store backorder information, but I understand the best practice is to store backorder status returned from EDI PO Acknowledgement in a DFF. I don't see where to load data in this field outside of UI, nor where to retrieve it from database, nor where to see this in UI such as in SSP.

Appreciate any insight into how others are using this field.