On 2 Sep 2005 05:17:04 -0700, "martin"
wrote:

I understand that a ticket on NR trains must be valid for every station
at which that train stops.

What you're saying doesn't make much sense - ITYM "a zonal ticket must
be valid for all the zones you pass though".

I've also had a quick look over section K
of the National Fares Manual about Travelcard extension fares (although
to be honest, it scares me).

"Customers" aren't supposed to (need to) read the fares manual... just
ask at the ticket office and they should sell you the best ticket for
your journey.

I've currently got a Zone 2 travelcard on Oyster. I've also got a
Young Persons Railcard.

I want to travel from Kensal Rise (zone 2) to Acton Central (also zone
2); this train's only intermediate stop is Willesden Junction (zone 3).

What kind of ticket should I ask for at the booking office,

Just describe the situation and they should know what to sell you.

how much would it cost me,

This is a bit of a long one, due to the fact that Tube and NR fares
are both valid on the NLL.

The correct extension ticket on the Tube farescale would be a Zone 3
single, costing £1.30. However, I'm not sure whether the ticket office
at Kensal Green is able sell the full range of Tube fares (and in
particular, Tube extension tickets).

The correct extension ticket on the NR farescale would be a single
from the last station your ticket is valid to (Kensal Rise) to the
first station where it becomes valid again (Acton Central) - so in
this case, it'd be a single for the whole journey. Which also happens
to be £1.30. Except that you can use your Railcard for NR fares, so
you'd get it for around 90p.

and what kind of proof would I need to show of what's loaded onto my
Oyster card?

Just wave the card at them - if they want proof, they'll have to use
their hand-held Oyster reader, if they have one. The extension ticket
would be issued on paper anyway.

Now, for a slightly tricker one: Acton Central to Harringay Green
Lanes. With this journey, the train leaves zone 2 on three occasions
(at Willesden Junction, Hampstead Heath, and Crouch Hill, just before I
get to Harringay).

Right. You have 3 "gaps" to cover. The first 2 could be covered with
an LU zone 3 ticket extension, or with separate NR singles from Acton
Central to Kensal Rise and Finchley Road & Frognal to Gospel Oak
(though no doubt a single from Acton Central to Gospel Oak would be
cheaper). The last one would be covered by an NR single from Upper
Holloway to Harringay GL (Tube singles aren't valid, and Boundary Zone
tickets are only available to destinations outside zone 6). HOWEVER,
it's highly likely that a single from Acton Central to Harringay GL
would be cheaper than any combination of the above, so that's what
you'd get sold instead.

or is this a case of combining a Z2 7DTC with a Z3 ODTC, and entirely
confusing any conductors I happen to encounter?

ODTCs are only available in z1-2, z1-4, z1-6, and z2-6 flavours.