I did not see your post, but you did not say anything wrong! In NY State, there is no blade lenght written in the law, and a single edge fixed blade that does not have a weapon blade design ( tanto, dagger, bayonet, kriss, etc) is OK to carry anywhere but NYC. In NYC, it is OK as long as it is NOT exposed and under 4". In all of NYS it must not be carried as a weapon ( including self defense). You need not have a direct need to carry it, but I suggest you have one thought up to say is your intended lawful reason for carrying it.
I assume you have been shopping on Sunrise Hwy, at the Swordsman shop? Nice guy, but not too sure he is 100% up on the law. He has the case law about how balisongs are not gravity knives, but they are considered dangerous knives ( same charge).
Under what conditions have you had knives taken off you? Why where you stopped? Searched? Did the police threaten you with arrest if you did not allow them to take the butterfly knife ? Nassau County? I ask this since as a former NYC LEO and Nassau resident with a 16 year old son, I am curiuos how your losses came about. The Nassau PD once stopped my son and his friends for being in a park at 7 pm ( twilght in September) saying it was after dark and they were not allowed there. They searched them and found a small folding knife my son carries on him. It is a totally legal knife that you could not flick open ( I can't and I can flick open anything). The officer told him it was a switchblade! The officers threaten them with arrest for tresspass, and my son for the knife. They called the parents and I was there in two minutes. The officer asked me if I was aware my son was carrying a knife, and I told him yes, that it was legal, and I am a former Captain from the city, so I know the law. He quickly gave me the knife back ( from his pants pocket were he was most likely going to keep it). I am not knocking the Nassau PD as I find them very polite and responsive, and police everywhere treat teens in a different manner than any other age group ( I know I did). I am just wondering why you had so much trouble?