Logic for handling shaping points and via's on 590LM

Can't see a device specific forum so hope it's okay to post some questions about my 590LM in here.

Q1: Can anyone (ideally a Garmin developer) explain how the 590LM establishes it has arrived at a 'via' on a custom route? Does the device for example, need to pass within a certain distance of the via, and if so, what is the distance/radius?

Q2: Can you explain the logic/rules for how the device handles missing a) one or more shaping points and b) a via.

From my own testing, it seems that if I go in a different direction from a single shaping point, the device doesn't take long to abandon it [the shaping point] and re-route to the next point on the route, but if my detour mean going in a different direction from two shaping points, it tries quite hard to turn me around and only when I rejoin the original route further along the original route (past the missed shaping points) does it then re-route and carry on. With via's, it never seems to give up on them and tries to turn me around.

Q3: Does the 'Skip' function work on shaping points and via's, or just via's?

Q4: Is there any way of getting the 'Skip' function to ask you/show you which via/shaping point you are skipping?

Q5: Is there any way of reviewing progress on a custom route to see which shaping points you've already passed? I've looked at the route in trip planner to see if shaping points (and possibly via's) grey out once you've passed them, but they don't seem to.

Sorry for all the questions.