mcp wrote:

New Cross, Waterloo East, and St Pancras Low Level use letters rather
than numbers for their platforms.
Each of Waterloo East and St. Pancras I can understand as they're just
about two stations on the same sight, New Cross, I've never been to.

It's to avoid confusion with the platforms at nearby New Cross Gate.

By the way are the New Crosses a valid "outerchange" station? Thanks to
Overground there's a potential increase in interchange traffic that
previously would have gone via London Bridge.

In fact is there a clear list anywhere of which pairs of stations definitely
are and aren't valid through interchanges on a single ticket?

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