I would highly recommend looking up the actual state laws on the matter.
I can definately tell you that cops either won't know or will deliberately lie. There may be exceptions to this rule of thumb but I've never personally encountered one.
DAs are only slightly better.
NC is a shall-issue CCW state; in general, having a gun carry permit will *usually* make cops leave you alone on knives, if the gun permit isn't also a "general weapons permit" such as in AZ. But that's rare.
Jim