Is it possible to obtain the same legendary item from the same boss on successive kills?

When farming an enemy and you get a legendary from an enemy (Killed Rakkman and you get a Gunerang out of him) when you kill that specific enemy again straight after you save and quit, is it certain that you'll get the legendary again?

There is definitely not a guaranteed chance at the same legendary weapon; the pseudorandom number generator isn't nearly that easy to fool. I have farmed many many bosses for less than many many legendary weapons and I'm not sure I've ever seen the same weapon spawn successively, and it certainly doesn't happen every time.

You can still get the same legendary a second/third/nth time around, but whether you do or not is completely random based on the boss' drop rate.