They tried to give me the "RCI exchange reservations aren't eligible for early booking" line too, but after waiting for an hour to speak to someone, I wasn't inclined to take "no" for an answer. I asked politely if she could double check that, and said that I knew of other people who had done this successfully (thanks
@marsh0013!). I'm not sure she believed me, but she decided not to argue (she was actually very friendly). Another hour waiting for IT support, and I am finally confirmed.
I'd guess that what's actually happening is that the CMs have been told that incoming RCI exchanges
by non-members are not eligible to attend, and that has gotten generalized to "RCI is not an eligible booking". I could be wrong, but I don't know why they would restrict it otherwise.
I probably could have waited until they opened registration to all members, but we're attending the first (March 21) event, so touring plans are pretty well set for the week. If I didn't get in I would have had to rethink everything!