I'm struggling to see how book between 1 Feb and 5 Feb reasonably means book between 1 feb and 20 jan next year.
An IT glitch making this work does not make it reasonable to think that 1 - 5 feb includes 6 feb to 20 jan.
I sure a lawyer could reasonably make the case that delayed booking to gain a benefit against the conditions is fraudulent.
The problem is, you are not reading the T&Cs, or even what other members are saying. Nobody said "book between 1 Feb and 5 Feb" means "book between 1 feb and 20 jan next year" (obviously).
The relevant clause in the (amended) T&Cs states: "
Flight gift vouchers purchased but not redeemed for an eligible flight booking during the promotion period will not earn double Status Credits."
As I'm sure you will agree, there is no mention of
any specific dates in that clause. Are you with me so far? That's the crux of the issue.
This means we have to know what "the promotion period" means in order to interpret this clause, but QF has failed to define that in the T&Cs. However, one perfectly reasonable interpretation is that the promotional period is between 12 February 2018 and 20 January 2019, as those are the dates when travel must be undertaken in order to be eligible. Therefore, it is perfectly reasonable to interpret this clause as saying "if you use a gift voucher, it must be redeemed for a flight that departs between 12 February 2018 and 20 January 2019".
By the way, aside from the ambiguity about what "promotion period" means, there is also a further source of ambiguity: the "during the promotion period" part of this sentence could refer to either (a) the time of redeeming the voucher or (b) the time of the flight.
In summary, QF's T&Cs are so badly written that they are meaningless, so there is no possibility of QF taking action against anyone who has purchased vouchers for use with this promotion. The other way around is potentially a different story though.