Beric was rescurrected rather quickly after his deaths but lost more and more of himself as time and the revivals ran on.
Cat was dead for days before they found her body. Stoneheart seems to retain some of Cat's memories, but has lost much of who Cat was as a person.
Perhaps Martin's goal in Jon's Ceasar like stabbing was to kill the standard hero of the story and replace him with something darker?
Were other forces at work in Jon's final POV? Mel? Bloodraven? Bran? I don't know.
It could all just be a feint. Was the slash to the neck just a nick or did Jon sustain a more grievous wound than he realized? Would his layers of wool, leather and perhaps chainmail protect his abdomen? Would the knife in the back paralyze him? Is that why he did not feel the fourth knife?
A friend pointed out to me that Martin's characters never die in thier own POVs. (Cat got brought back.) I will know Jon is dead when Mel confirms it. She is the only other POV character we have on the Wall, right?
My personal pet theory (of the day) is that the Others are coming which is why Ghost was flipping out. Jon is dead, and the Wall is getting ready to fall.