I've said it many times before, but I'll say it again...

DON'T PUT DATES ON OWE TICKETS!!!!!

Why have all this hassle? Just get the tickets issued as "OPEN" then deal with the reservations separately. A or D class bookings can be made directly by the airline or a TA independent of the ticket type (I've never had any problem waitlisting). So long as when you turn up to check in you have a reservation in the correct (or lower) class and a valid open dated ticket there will be no problem. I have never had a problem being standby or changing reservations at checkin if seats were available.