Originally Posted by
pcolmer
Really? I'm sure I was told that once I'd booked a flight with a companion voucher, I couldn't add a flight to it afterwards.
The person who told you that is wrong.
In particular booking an outbound when it becomes available at 355 days out and later adding the return when it becomes available is a very popular tactic for using a companion voucher - there is a list of previous threads where this tactic has been discussed in
nux's post here
http://www.flyertalk.com/forum/25848030-post3.html.