3185 vs 3186 vs 3187

[jstan9]

Hello TRF members. I have a 3 month-old GMT BLNR Batman, and know it's using a relatively new 3186 movement, itself a refinement of the venerable 3185.

I've always admired the polar Explorer II but think the new 42mm size is too big for my scrawny wrists (my BLNR wear big, and I love it, but I don't want lugs over-hanging my wrist). In ogling the Explorer II rolex site I noted that it used a 3187 movement.

This may be a dumb question, but does anyone know why it wouldn't use the same 3186 as the GMT? Itself using a fairly updated reference? Thanks in advance!