Fishy, a cyclone can be legal if it is marked 177 because they round up. you are 1 gram over. It is not giving you a distinct advantage. The illegal discs that I have issue with are the guys who brag about throwing 180g wizards to fight the wind.
Illegal weight discs can be used in your casual play, they are only going to come back to haunt you if someone sees your disc upside down and they happen to know the max weight of that mold.