I've had mixed results for ATL-SJU. In April, I went ahead and cashed in credits to secure the last two BC seats since my odds were not looking too good. For the return trip there were more seats showing available. Since I was the first on the check-in list I took my chances and was upgraded complementary. I would watch the seat maps very closely as your dates approach. According to the GA''s, SJU BC typically sells out.