"MIG" wrote

It's not currently possible to get from the Chiltern Lines to the
stations between Harrow on the Hill and Moor Park, incidentally.

If they ever did stop at those, was there a different track
arrangement, or were there more platforms?

Before 1960 it was only double track between Harrow and Watford South
Junction, so all trains (BR and LT) passed platforms at intermediate
stations. It is possible for a train from Amersham to cross to the slow
lines at Watford South Junction (and some LUL trains do so), though Chiltern
trains are not authorised to use the slow lines. So a passenger travelling
from north of Amersham to a station between Moor Park and Harrow has to
change twice, or double back from Harrow.

Peter