In the vendor add form, there is a yes/no field labeled "Tax number registered". It maps to aqbooksellers.gstreg. I don't think gstreg is used anywhere. Bug 12839 removed any reference to this field in the code. Having yes or no in this field doesn't affect tax calculations. I wonder if some libraries use it to indicate something internally? To access: 1. Go to Acquisitions 2. Click 'New vendor' --> 'Tax number registered' field in the 'Ordering information' section