Steve M wrote:

There are two sidings at Victoria and one at King's Cross. It's not
uncommon for trains to terminate at the former and reverse, and I think
(although I'd have to check the WTT) that there is one train a day
scheduled to use both. Late evening if I recall correctly...

On TfL's ETA site for the Victoria line I have seen a train destination
of 'Walthamstow Sidings' - as opposed to 'Walthamstow Central' for a
normal terminating train returning south.