wrote

True. I just wondered whether there had been any perceived diminution
of reliability by Cheshamites used to a self-contained yo-yo-like
operation not subject to the potential for delay which would be more
prone to afflict the odd "through" journey and where the frequency is
low enough to make reference to a timetable a more likely thing than
many other parts of the LU network.

I suspect that delays on through trains now have to be balanced against
times when connections were broken at Chalfont to/from the shuttle.

Peter