Don't think it's related, since the OP was talking about pins v screws. However, it seems you're asking about the structural part of the CBBL, and why there are 2 screws (actually 4, 2 per side) threaded into it for the M2 but not the XL. I'm only speculating, but it looks like Spyderco sought to limit how many fasteners were used on the XL. Because the M2 is shorter, those two screw locations can serve (along with the lanyard tube) to hold the scales together. However, on the longer XL, there would be too much unsupported length along the spine of the knife. So, Spyderco added a standoff in the middle, and thus added a screw location. To avoid increasing the number of fasteners, Spyderco provided some other internal means of fixing the structural part of the CBBL.