"77002" wrote

Yes, I recall the short trains. The four car units had cabs at both
ends. The three car units had a cab at one end. Daytime services
were four car only.

AIUI the A stock were always in 4-car sets and originally had operative cabs
at both ends. Until quite recently a few units were kept with operative cabs
at both ends, to work the Chesham branch diagram, and they were also used in
4-car formation when they worked the East London Line. But for many years
most units have had an operative cab at one end only, so have been used
exclusively in 8-car formation.

Peter