Originally Posted by
BA or bust
...It is a concession and occasionally you get an agent (if you are calling) who does not ‘know’ about the concession in which case best thing to do is HUACA. IIRC that is the only concession, which I think means you can’t add a flight whenever you want later.
I think you're maybe conflating a couple of things?
The concession is that if you couldn't book the return at the time of the outbound (as past 355 days) then they don't charge the change fee. If the return (regardless of availability) was in the booking window at the time of the outbound booking then a change fee will be due to add it.