Yes, the contacts advance with the waypoints you plot (a really nice featur4e by the way
). The contacts might have gone into a port before getting to where you want to intercept, or changed course if they have a dog leg or non striaght course or even if you were seen, been diverted away from your position. The traffic in the game does actually divert away from you fully with a complete permanent course change, not like before when they just steered madly for a bit and then went back to their original course. I find that if the contact is close, I can usually get there and intercept, but if it's far away, then I can't usually intercept it. The best way I have found to intercept is to steam directly towards their course line and then turn in, and head straight at them. This should in theory give you the best chance to intercept them along their track. Good luck!