JOOI, what're these based on? I'm sure the off-peak pattern tilts
towards Edgware-Kennington and Barnet-Morden, but maybe I'm suffering
from false consciousness...

I thought it was the morning peak that shifted that way. *There is a
continual announcement at Euston, with a strange mixture of 24-hour
and 12-hour clocks, that "between 0730 and 10 am" all trains to
Edgware are from the Charing Cross platforms and all trains to High
Barnet and Mill Hill East are from the Bank platforms.

In the morning (about 07:20) it seems all trains from Totteridge and
Whetstone are via Bank to Morden - fortunately my destination is
London Bridge so that's ok. In the early evening (abut 17:15)
departures from London Bridge are split about 50/50 between Edgware
and Barnet (although they seem to be timed so I always just miss a
Barnet train)

Peter