In message , James Farrar
writes
So why isn't prepay valid for all stations out to the end of Zone 6?

Because prepay is only available on National Rail for sections of line
where Underground fares apply; essentially this is any section that
could, as an alternative, the passenger could travel by LU services.

Thanks. The more I hear about the restrictions on an Oyster the more I
believe it is a total waste of time & effort.

--
Bob Adams