Garmin navigation - starting a route from a different start point

Is this definitely how Garmin nav works, or are you formulating a hypothesis (I genuinely don’t know).

So, if I load my 100km race map onto my Garmin, but ride to the 50km point first, will it navigate me onto the course from that point if I say no (to “navigate to start” or whatever it says)?

Thanks heaps :crossed_fingers: