Back in the days before flat fares, buses knew roughly where they were -
they needed to know what fare stage they were in for the machine to price
the tickets. I think the driver had to push a button every now and then.
There's currently some sort of beacon system on some routes, for tracking
buses, but i don't know if it tells buses where they are.

I noticed from observing a recent bus ticket machine, they still retain
their fare stages, but only the final one is displayed and the driver
didn't change the stage. So, any ticket issued would have been valid
Cockfosters Stn (start of route) to Aitken Drive (end of route).

As to getting FOI informaton, not sure. I was able to retrieve total
passenger numbers for Local Authority contracted bus services (outside
London) - but obviously getting bus passenger data is easier.

If you select the line name from the left-hand side menu, you can see
passenger numbers. ISTR seeing actual statistics of station usage on the
site somewhere, but can't seem to find it.