I'm stating the obvious, but that's why it's expedition 33, not 69 or whatever [endgame spoilers]

!Verso died on December 33 (the "real" world here is still a fiction), and the whole painting is about holding on memories of Verso. So yeah, it's a nice number (not as nice as some though), but the point is the number of the expedition is connected to the date of Verso's death, in case someone missed it.!<