So during the KX works, Euston to KX is an allowed out-of-station
interchange?

From what's been said, I gather that the situation is:

- the gates at KX (subsurface) and KX (deep level) allow
out-of-station interchanges (so that you can transfer between the
two);
- the gates at Euston tube and Euston NR (and also Euston Square?)
allow out-of-station interchanges (same reason);
- an out-of-station interchange can be made between *any* two gates
that allow them - not just between "linked" pairs/sets of gates.

So presumably, if you touched out at Hammersmith, got a (super fast)
taxi to KX, and touched in there, it would count as an out-of-station
interchange.

So is there a list of places that allow these interchanges? The Baker
Street / Marylebone one is far from obvious (it's not shown as an
interchange on maps, though there are signs at Baker St pointing the
way to Marylebone), and I can think of some other places it'd be handy
(Northwick Park to Kenton?).