One thing that surprises me is that in such a ROM-constrained context, the artists weren't asked to save some more. There's some tiles that are empty except for a handful of corner or side pixels; I could imagine going to the artists and asking them to tweak the pose a tiny bit to save a tile.
Or maybe what we're seeing in these sheets is the result of doing that just enough to fit their game into the available ROM, at which point they didn't need to free any more tiles?
My guess is that they preferred bigger optimizations first, such as the given examples of reusing Ryu's body tiles for Ken and mirroring Sagat's legs. If those hit the target, there's no need to go around trying to pick up a tile here and there around the edges.
Also, any given saved tile might not have packed well in the overall sprite sheet, given that they were organizing the ROM by hand.
One thing that surprises me is that in such a ROM-constrained context, the artists weren't asked to save some more. There's some tiles that are empty except for a handful of corner or side pixels; I could imagine going to the artists and asking them to tweak the pose a tiny bit to save a tile.
Or maybe what we're seeing in these sheets is the result of doing that just enough to fit their game into the available ROM, at which point they didn't need to free any more tiles?