The more I read the T&C on the register page I note multiple references to the "Promotion Period" which is set as 12 Feb-20 Jan. The gift voucher line states "Flight gift vouchers purchased but not redeemed for an eligible flight booking during the promotion period will not earn double Status Credits" yet later on ". Full or part travel of an itinerary is eligible only if you book and travel within the promotional dates as listed above. If you change or cancel your initial qualifying booking and/or travel is completed outside the promotional period, this bonus offer will not apply.
I think as usual the wording is poor as it can be interpreted a few ways, but the other references to promotional period refer to the travel dates.
I consider it equally valid a notion that a voucher purchased but not redeemed for an eligible flight booking during the promotion period means just that... What's the opposite? a "voucher purchased and redeemed for an eligible flight.." would earn which is the expected behaviour. It does not mention the booking period(Feb 1-5) but the PROMOTIONAL period.
I think this just enforces the current logic of a flight booked to fly within the promotion period is eligible...
but I am open to thinking the other interpretation is obviously possible, but if it was I think it should say "flight gift vouchers purchased during the promotion booking period, but not redeemed during this period, are not eligible.
I think there is wiggle room here. Of course it's how QF Loyalty are going to interpret it that matters, and the wording suggests what we think they mean... so we may well see in a few weeks if it's true or not when someone actually tries it in anger.