I'd say one only needs to know X and Xsub for the knife. And for that, you could do the following: calculate the usual stuff (time left before it spawns, speed), then find out how long ago the last interrupt happened, predict how many frames will be eaten by the future interrupts before the knife spawns (rather easy actually), and then tell what will be the speed and when. Iterator isn't needed: once the tosser spawns, it won't use spawn iterator for knifes. Direction can also be predicted by RyuX - BitchX and spawn timer easily.
Warning: When making decisions, I try to collect as much data as possible before actually deciding. I try to abstract away and see the principles behind real world events and people's opinions. I try to generalize them and turn into something clear and reusable. I hate depending on unpredictable and having to make lottery guesses. Any problem can be solved by systems thinking and acting.