I remember direct trains from Charing Cross to Bromley North in the
morning peaks in the early 1990s, but that's against the rush hour
flow.

So they were effectively empty stock workings anyway, like some of the
current runs to Hither Green or Beckenham via Catford Bridge. The
reason why these call at a couple of stations rather than just running
empty may be to cover the other rush hour flow from Waterloo to London
Bridge.