Can somebody please remind me of current policy regarding buying add-on
tickets from Boundary Zone 6 on the GN (which don't exist these days, they
are issued from Hadley Wood, the boundary station) to stations beyond,
specifically Huntingdon/Peterborough, when purchased as add-ons to an
all-zones season ticket Travelcard?

*Is* it necessary to stop at the boundary station when making such a
journey? My understanding had always been that it was not, which was borne
out by the number of times that I've bought them, without problems, over the
years and had them inspected - without question. However, I recently had a
run-in with an over-zealous ticket office clerk at King's Cross, who refused
to sell me an add-on to my season ticket and insisted that I should buy a
King's Cross to Peterborough ticket instead. After I showed him the return
half of the previous one that I had bought and never been questioned on, he
capitulated.

The whole boundary station issue has been clouded for as many years as I've
been travelling. In the seventies, it was necessary to stop at the boundary
station between two tickets, in the eighties it was not necessary (certainly
from BZ6, although tickets were then issued as Boundary Zone 6). My
understanding of the current situation was that it was necessary to stop at
the boundary station when "transferring" between two tickets, except where
the ticket is an add-on to a season ticket. I've never had any previous
problems on the GN, or on SouthEastern, South West Trains or any other TOC
when buying an 'add-on'. Who's right?