here's what I would do.
call QF due to them cancelling flights request a Travel Pass with DSC (pre other threads). they are obliged to do this on a fare they can refund per their cancel rules (and QF would rather issue a Travel Pass than give a refund - and DSC is one of the current offers). Thus you can then re-book for whatever flight and get DSC (valid till 12/22).
However if you have chosen to cancel to a credit voucher - your DSC should stay with the voucher because the PNR stays the same.
So either way you would be covered -unless of course you just cancel and refund the booking.
Ah, that's fantastic advice - thank you! Will using the 'Cancel/Voucher' button under the 'Manage Bookings' menu mean l would keep the same PNR when l use that voucher on another booking?