I'm with ExMo on this. Particularly with an open-dated ticket you should have absolutely no problem checking in for the QF flight with the ticket as is. As with ExMo I have done this a number of times on other routes and never had a problem, except in HEL where the AY check-in desk insisted that I walk 10 yards to the AY ticketing desk to get a sticker put on the coupon to change it from AY to BA (or vv, I can't remember now). There was no charge for this.