Fields not showing in AIF Service Schema

I've modified the SalesSalesInvoice Service Query (AxdSalesInvoice) to include the CustTable. The CustTable has fields such as 'DEL_ZipCode' but when I update my service document in tools and then refresh my AIF Services and view the schema, the field isn't there. It's the same for other fields, it seem's to only include certain fields from the CustTable, is there something I have missed? I've also noticed the same in the standard AxdSalesInvoice query. It has a field in the CustInvoiceJour called 'InvoicePostalAddress' or 'DEL_InvoicingAddress' but this isn't in the schema either