Flew eze-scl-ccs//bog-scl-eze-jfk on LA in Nov/Dec on a Oneworld RTW 1st class ticket. Generally, they were more forthcoming in releasing an A class seat than AA from South America to North America and within South America I had no problems getting a confirmed A class reservation. ITN gives A Class availability on Lan Chile although I didn't always find it to be particularly accurate. You may find that on certain days of the week, no seats are released for A class bookings until very close to departure date. My advice would be to always have the ticket issued in A class even if it has to be issued as an open segment and confirm in D class and waitlist in A. At least you won't have to argue with airport check-in about what class you are entitled to fly if a 1st class seat is available on the day.