This is the NM forum, not CO. NM does not have length specifications.
So, according to the following...:
NM 30-1-12. Definitions.
As used in the Criminal Code [ 30-1-1 NMSA 1978]:
A. "great bodily harm" means an injury to the person which creates a high probability of death; or which causes serious disfigurement; or which results in permanent or protracted loss or impairment of the function of any member or organ of the body;
B. "deadly weapon" means any firearm, whether loaded or unloaded; or any weapon which is capable of producing death or great bodily harm, including but not restricted to any types of daggers, brass knuckles, switchblade knives, bowie knives, poniards, butcher knives, dirk knives and all such weapons with which dangerous cuts can be given, or with which dangerous thrusts can be inflicted, including swordcanes, and any kind of sharp pointed canes, also slingshots, slung shots, bludgeons; or any other weapons with which dangerous wounds can be inflicted;
...if I do great bodily harm to you with my 3 or 3.5" knife, I have in fact used a weapon, and a deadly one at that.
Check your facts before making generalized statements.
I would tell him about it because there is no harm in doing so. The less surprises when you have been pulled over by an officer, the better.