Stratford - huh?
 

asdf wrote:

There's a big sign by the departures one at Bank that talks about "if
you're going outside your zones", so I think it's for people who have
a Travelcard and have arrived from somewhere ungated where they don't
need to touch in (Waterloo W&C?).

Coming from Waterloo W&C, you'd have had to pass through the gateline
at Bank W&C, wouldn't you?

I don't think so, although I normally interchange there (invariably only
between the W&C and Central) by going via the ticket hall. But my
recollection is the old gateline at the end of the interchange tunnel has
been removed, now that there's one at the foot of the travelator & stairs. I
presume either the entry hole at Waterloo is now not considered a
significant problem on the system or having a Stratford style internal
gateline would cause too much congestion.