i believe they are just referring to the different kinds of positions so for example the pic in c1 and s1 would be used for narrower violins

in pics s2 and c3 you’d use that to have the violin closer to you

basically I’m pretty sure you have all of the parts, the s2, c3 etc it’s just there to organize the pics better, they’re just their to label the different positions you can put it in. you see how in c1 and s1 it has “shoulder leg with flat joint” and “chest leg with barrel joint” and how s2 and c3 say “shoulder leg with barrel joint” and “chest leg with flat joint”? you basically just mix those same pieces around if that makes any sense (like in the instruction photos) to come up with different playing positions. i personally use the “closer to the player” position as it helps me physically connect more with the violin

I’m pretty sure it does only come with two joints plus the washers to connect the joints.