John, There is no difference which I can see between the #18 and the #14 with teeth.
I don't
know for sure why the #14 has the spear point when teeth are added, but I will take a stab (so to speak) at it.
Look at the spine of the blade on a model 14 between the hilt and the top bevel. There is only appx. 3" from the hilt to where the top bevel begins. Now remember that the teeth are the last operation before the knife is final polished, honed, and packed for shipping.
The teeth are ground into the blade, free hand, with a thin grinding wheel. I do not know the diameter of the wheel but I would guess at 6", but even if it is a 3" wheel there must be clearence between the hilt and the grinding wheel when the teeth are ground at an angle, so you can't start the teeth close to the hilt. You also can't grind into the trademark. The teeth have to begin forward of the trademark, which would leave less than 1" between the trademark and the start of the front bevel. You want a sharpened top bevel in a fighting knife.
The Model #15 grind is identical to the 14, just shorter. It also has a spear point when teeth are ground into the front portion of the blade, about 2".
If you put the teeth into the front of the #14, no sharpened top bevel...so the knife is given the spear point grind of the #18 to allow retaining the sharpened top bevel.
As I said, I don't know that that is the reason for the grind when saw teeth are put into the #14 but it makes sense to me.
Regards, Doug