I probably need to read the legislation but I wonder exactly what that covered and what exemptions or exceptions there may have been? Growing up from a farming background and living rurally I always had a pocket knife of some sort or another. Just about everyone else did as well. I know I bought some long after 1991 where the blade locked in to place. I've also got one or two garden "multi tools" that include a blade that locks in place. Again I wonder if perhaps those aren't covered? In any event if the legislation was introduced in 1988 there will still have been large numbers in circulation in 1991. I doubt too many threw away what they already had.