"SYD/MEL - £849 when booked on ba.com - valid on BA and QF metal - requires 21 day advance"

It seems very restrictive to have a 21 day advance purchase requirement on a fare that is only available for departures up to 30 days away = 23rd June. Does this mean this fare is only really available on BA.com for departures between 14th June and 23rd June as of todays date = 21 days away?? This seems to be a pretty pointless sale unless you are travelling in one specific week in June. Or am I reading the terms and conditions wrongly?