Don't quote me on this, because my product knowledge is waaaay behind. And things change quickly.
C.F. Martin & Co. in their classic style of confusing everyone who isn't a total guitar nerd, [raises hand, sheepishly] offers two nearly identical guitars; M-body, and 0000. The key difference being scale length. M (Coz' likes the Style 36, and I agree, quite a sweet axe) comes with the same long scale as a D, 25.4". The 0000 comes with the shorter scale, 24.9".
Same thing happened with the long-scale but small body OM (Orchestra Model) and 000 back in 1933. (yeah, this has been going on for a while) Somebody decided hey, this 14 frets clear of the body is a cool idea, might even catch on... but... how 'bout a shorter scale like our 00 guitars? Nah, that's just crazy talk... nobody wants that! For a short time, they made two identical guitars stamped with different models though. (they're worth a fortune now)
Now they are both a standard. That extra half-inch of string-pull seems to make a difference whether we are aware of it or not. I kinda' wish I didn't know. Me and my OM-18 are having a spat over it. Some days... I wish it was a 000. But we got a history together.