1968 was the year Congress made carrying a concealed weapon on an airplane a felony. That's the main one.
And if you can show to me that it is worth my while to take the approx. 12 hours I estimate it will to look at every single hijacking on that site individually to make the new graph, meaning that you will NOT respond with the immaturity and avoiding the facts that you did the last time, then I will do so.
In the meantime, I'm going to see if I can find a source that has the data collated to match what we need here so maybe I won't have to go through all of that.