https://pro.delta.com/content/agency...et-stock-.html
Virgin Atlantic Flight Segments on Delta 006 Ticket Stock Effective January 10, 2017, Delta will allow an itinerary with all Virgin Atlantic (VS) flight segments to be issued using Delta 006 ticket stock.
Other Carriers Allowed on Delta 006 Ticket Stock
Currently, Delta allows a ticket to be issued using Delta 006 ticket stock, if at least one flight segment contains a Delta (DL), Air France (AF) or KLM (KL) flight segment. Certain exceptions may apply.