I flew out of South America for years (767) and I guess I'm trying to figure out what you're asking. If the cargo weight, fuel, pax load, etc. puts a flight at MGTOW, then what difference does it make how many seats are available ?

On a lot of my flights, in both directions, we were often full and couldn't accommodate SA's no matter what the weights were.

If you're a new hire, the first rule of Int'l travel is always have a back-up plan, whether an ID 90 or a ZED ticket along with flights on other carriers and/or other city pairs. If not, take some extra clothes and a lot of money.

G'Luck Mate