Grizzle necklace

I have been told that dogs with a "dirty neck" or "necklace" are grizzle. Do all grizzle Norwich have a necklace?

Some pictures of "necklaces":

Black-and-tan Norwich also can have necklaces, although I am told that most do not.

According to folklore, a black-and-tan Norwich with a necklace will retain their black saddle; while a black-and-tan without a necklace will "grizzle out" (their black will turn grizzle or even red, although you can still see the black when the dog is stripped out).