wrote

When it 1st electrified, (Nov. '60, when I were but a young lad....)
it was 6 tph off-peak & 9 tph in the peaks.
Train were probably longer too, 6-car off-peak & 9-car peak.
'Twas before the Victoria line opened, so perhaps that stole some of
the traffic?

Indeed it did. When the Victoria Line opened Chingford went down to 6 tph
peak, 3 tph off-peak (so the off-peak service is now more frequent than it
was in the 1970s.

Peter