Paul Corfield wrote:
I may be horribly out of date but here goes.

snip

I confess I don't know quite how the interavailable routes work - i.e.
where LU fares apply and the TOC has to get a share. I would imagine
this is based on a composite of sales and ridership surveys. The
existence of ticket gates at places such as Fenchurch Street will
provide some extra data as to journey volumes.

This is the part that I'm most curious about - whilst looking this up
in u.t.l. I came across a thread where someone vehemently stated that
Chiltern receives no revenue whatsoever for trains that run to
Aylesbury via the Metropolitan Line, while someone else stated in equal
fashion that they did. I wondered which statement was true.

Obviously, as you said, the presence of ticket gates and Oyster pads
makes collecting the necessary data much simpler, and thus the revenue
sharing probably follows the actual usage much more closely.

snip