Interesting thread - thanks for the graphic gemma. I would comment though that the blue sstuff doesn't look much like 'track crawling'. With the sort of landmarks available on this route student X should have been able to get on and stay virtually on the line exactly if they genuinely were track crawling.
Instead it looks like there was no line and no clear idea of what the desired direction was. That could still have worked whereas the blue line looks like there was little spare capacity for thinking about what the track line looked like and what features would confirm student X was heading in the right direction.
From my experience the only useful thing about having a line is that it makes that point very clearly.
The other item you might think about adding is trackmarks with timing. They can work almost as well as a line and if used as well as a line they give a very clear indication of the last 'known' position and its time - which makes ETA and other estimates child's play to make.
At the end of the day student X should have aan overall 'picture' of where they are and were they are going. DR tends not to do that until turning points, pilotage or track crawling can do it nearly continuously - as can GPS or VOR cuts or other mutiple radio aids. Combinations of these methods can eliminate all the potential errors and ensure you always know where you are. Single methods all have potential pitfalls.