Thanks. Actually I couldn't find a way of asking VS anything (seemed to be endlessly looped around self-serve help centre) but KE's live chat was really helpful: connected quickly both times I contacted them and able to find the reference immediately. They expressed surprise that VS hadn't told me it.

Another quirk is now that KE won't let me see the seats I've selected unless I login (I am logged in) and it seems that I can only view them if I change the loyalty number on the ticket from VS to Skypass. But VS website shows seats selected so it seems to have worked.