Duncan wrote:

"The return portion of these tickets is restricted if you join a
northbound train within area B of the London Travelcard Area
on the route map overleaf, but is unrestricted if you join a
northbound train in area C or D."

Which should probably have read as follows:-

"The return portion of these ticket types is restricted if you hold the
return half of a ticket with the outward destination[1] within area B
of the London Travelcard Area on the route map overleaf, and the origin
within area D (or whatever it was), but is unrestricted if you hold the
return half of such a ticket with the outward destination within area C
or D."

I do not believe there is any scope within the fares system to
implement precisely what is being described above, as there may exist
Saver fares over which FCC have no control which may nonetheless be
valid on their services. I suspect they have simplified it to make it
easier to understand, but have instead introduced confusion and
theoretical loopholes.

The way restrictions work, the flow (origin and destination) is
important as restrictions are defined in those terms.

[1] I cannot think of a better wording. Hopefully you know what I
mean...

Neil