It may have a specific carrier printed in the box (I have had some with and some without) but that isn't a problem because it will also be endorsed "VALID ON BA/AA/CX/QF/LA/IB/AY/EI ONLY" and any of those airlines will accept the coupon. I have switched airlines many times on these tickets and never has a problem except once at HEL where they insisted that I get it stickered from an OPEN segment with BA in the carrier box to the dated segment with the AY reservation I had (or possibly the other way round). But this involved walking 10 metres to another desk and no charge so no big deal.