More han 30 years ago actually I think it was in late 1973 or early 1974...CAA trial flight during certificaion if I remember correctly. 3 crew, all dead, with their masks on.
The Oxygen valve sits in the empennage jus in front of the emer exit and can be frosted over, thus blocking flow. Therefore we used to switch on (pressurize the O2 System) in the before startup list. I have been flying with a lot of KA operators that wouldnt do that in order to save oxygen - you loose a little bit every time you switch it on or test it. Lot of system are a bit leaky too...in the old KA (prior BB1476) the O2 on and the mask drop handles were mounted overhead, same levers - so to prevent mistakes, some operators wouldnīt arm to. N777AJ is newer, the arming lever is beside the pedestal to the right, the "rubber djungle" is to the left. It comes with EROS quickdonning masks, housed in the overhead panel. The type that inflates the harness with oxygen pressure - which usually should be a sign of a pressurized oxygen system itself.
Had 2 windshields cracked in a B200, the most serious part of it was the soiling of my underpants. We even tried to crack it after it was off the airplane and we couldnīt smash it with the crash axe and a hammer. That stuff is sturdy.
The checklist was changed in this point years ago (maybe 8 ?) and I donīt recall wether the 4PSI was the old or new procedure. Iīm pretty sure you donīt have to dump.
If the video is right and the guys dumped and passed out then, they made a pretty stupid mistake. Their flying afterwards seems to be pretty well done. And part of the fame has to go to the best turboprop ever build, the rugged KingAir.