I don't know what part of NY you are in, but it may be that the New York City Administrative Code might prohibit double-edged blades. The City also restricts blade length to 4". As you pointed out, these things are no problem under NYS Penal Law.
I don't live anywhere near New York City.
"WARNING: The sale of all dangerous knives is restricted by law in the following states: New Jersey, New York, Michigan, California, and Illinois. A dangerous knife is defined as any knife having a blade of five (5) inches or more, or an overall length of ten (10) inches or more"
Now we're getting somewhere; the NYS Penal Code does state that a person is guilty of misdemeanor criminal possession of a weapon if he possesses any "blah-blah-blah, gravity knife, blah-blah-blah, metal knuckles...
or any other dangerous knife." Now, to my knowledge, a "dangerous knife" is never defined in the NYS penal code (since lawmakers love to use vague wording to expand what the law prohibits). I've no idea where this five inch/ten inch limit came from, as there's no explicit length limit listed in New York Law (at least not yet, and not that I know of).
I'm a folding knife kinda guy; I only recently got the fixed-blade bug, and thought I might get a classic. As of now, I own no "dangerous knives" according to the aforementioned definition -- and it looks like I won't be starting. I'm glad my lawmakers (and those of other states) are looking out for my best interests.
Finally, though, this starts to make a
little more sense, even if it's still just plain dumb.