Currently this is done via the Address Book page. The idea is that referring doctors might be either local users (already in the users table) or external, so the users table was expanded to support an "address book" feature. External contacts are readily identified as those having no username attribute.
i missed your post even though i have subscribed to the thread.
i tried your suggestion to use demographics-choices-provider as referring provider. it does populate field 19 on CMS1500 properly. i thank you for the clarification.
can i relabel that field as referring provider in demographics and create another field for assigned provider for that patient?