Ready to Fly doesn't know at that point whether you have flown the earlier sector, it doesn't carry the full ticketing DCS functionality, so it allows access, and indeed at that point nothing is wrong with the booking. At the DXB boarding gate the lack of a previous sector may have been more problematic but you may get away with it at that point, the auto-cancel isn't always immediate. The next day the rest of the ticket probably would have been cancelled.