Thanks for this! Just booked trips for my wife and I. Was about to completely cancel and rebook one for her at the same fare (to eliminate that age-old question about booking-before-registering) and a new one for myself.

To answer the other question upthread, historically you've been able to book the paid trip you intend to bring a companion on anytime you like. So, if you want to fly August 16th, you can book that part now. But you can't add your companion until August 15th. There must be a seat remaining on your flight, so if you literally want to fly on one of those first days of the promo, it helps to pick something you are relatively certain won't completely sell out.