There is a difference between 'cork 3' and the 'flat 3' aka the 'crooked backflip' off jumps. Usually executed with a japan or safety grab and usually most cleanly done on a hip. (Getting totally flat.)
Cork 3's were actually done when people were still riding long ass non-twin skis.
Clint Fiala and Kreitler had these dialed. Kids now get way more inverted on some Cork 3s and really style them out, but Clint is all tucked up in a little ball on some 220's on the cover of 'Boards in Motion back in 97/98. Twin tips didn't start the trickery, it just made it all easier.