I've been looking to modify an award reservation this fall for 3 people including myself that is entirely on LATAM (JFK-SCL-CJC-SCL-IPC-SCL-GRU-JFK). Everything is ideal except for the flights back. The SCL-GRU-JFK leg is on a Thursday, which we've been trying to push back 1 to 2 days. Using the BA search tool for LATAM availability I'm seeing something confusing.

If you search on eg Oct 14 for 1 person in business class from SCL-JFK you see 7 seats available on a SCL-LIM-JFK routing. If, however, you perform that exact same search but for 3 people in business class, the tool reports no availability whatsoever?