Good nav systems will fuse whatever inputs they can get including GPS, INS, compass, etc. in order to figure out and ‘snap’ to what road you’re on. Snapping to an individual lane is still AFAIK beyond these systems’ sensors’ capability. You will need an additional input like a camera for this that looks for lane markings.

Yes, they do that, and they rarely get that wrong.

Also, the better ones have inertial backup & flux gate for when GPS is unavailable. Inertial backup could also help to detect the signatures of lane changes and turns.

Try driving near a place with a lot of roads that are close together, like an airport. You’ll quickly see that snapping doesn’t really work, especially if you deviate from the route the GPS is trying to take you on.

I do this all the time and it works remarkably well. Amsterdam and the roads around it are pretty dense, up to 6 lanes each way in quite a few places with all kinds of flyovers and multi-lane exits.

At what speeds? I'm in NYC, similar dense road systems. At a reasonable speed, snapping still works because it knows where you came from. In stop stop stop go traffic combined with lane weaving and ramp merging I've found it is not hard to trick the gps into thinking you're on a parallel access road or unrelated ramp for a little while.

It's possible your highways are newer or less congested than ours?