I used to take my CRKT M16-14 knife on the nerd bird SJC<->SEA round trip twice a week. Nobody cared. This was mid-90s until just before 9/11. I didn't try to hide it - just tossed it in the bin with my keys etc.
Do you have a source for that? Because for as long as I can remember they have had to be checked, including in the 90s.
You always could, and still can, check a firearm into luggage on a flight.