Searching around in my dusty mental attic...
As I remember, somewhere back in the dark ages, one of the Guatemalan locomotives (I seem to remember it was #44) was laid over pretty badly. When it was rebuilt, it was decided to upgrade all the locomotives from soak to superheat and to install piston-valve conversion kits (hence the funny look of all three locomotives' valve chests). #40 and #44 retained their steam dome throttles; I have no idea when or where #111 got the front-end throttle.
I believe it was Phil Reader who told me that the #111 is a larger class of locomotive than the #40 and #44.
Other comments and criticisms appreciated.
Mike