Finally got through on the phone, CSR said they have been seeing a lot of this for the end of year/new year flights. They can add the companion.

I had preemptively booked an award flight for my companion, CSR was not happy with this and said not to do it! That it can mess up with security - cancelling, then rebooking a person on the same flight? I don't understand why, considering their website has a "change" button that allows you to rebook the same flight for less points/cheaper fare.