MIG wrote:
On Mar 8, 9:07 pm, Clive wrote:

What happened to zones A to D?

Not an expert, but they were replaced with numbers around about the
time of the creation of London Overground I think. Someone will be
along with the correct answer ...

That's how I recall it happening. The station maps were changed gradually
around the time of the LO franchise change, from November 2007 on?

Paul S