Yes, since the MX is so small you can often get 37 or 38 exposures. But.... The archivally safe three ring binder pages accomodate either 7 strips of 5 frames each, or 6 strips of 6 frames each, my personal preference. If you shoot 38 frames, what to do with the extra 2 or 3 frames?
As far as "overwinding," I suppose you could, but the resistance at the end of the roll is so pronounced its pretty unlikely. Just remember the first rule of camera use:
NEVER FORCE ANYTHING!
The MX is a delightful camera! Keep your eyes out for a winder. 2 frames per second switchable to single shot, and it adds just enough bulk and heft to the camera to make it just right, at least for me.
BTW, the real Achilles heel of the winder is the little screw which holds the battery compartment shut. Make sure it is there and still works. A design flaw by Pentax, the ME winder battery tray is much better, but the two winders aren't interchangeable.
Get out there and shoot and enjoy!