A "limited selection" (in
TfL» 's words when I asked them) of
NR» tickets are available from TfL machines at stations where
LUL▸ provide ticket issuing facilities on behalf of NR*. But in reality, it depends on what has been programmed into the machine. I understand someone has to manually enter the fares available for each station. At the ticket office, they can look up fares that aren't in their machine and manually (yes, manually) enter them into their computer.
My experience at West Ruislip (which is on the Chiltern line up to Birmingham Moor Street) would sell tickets to most Chiltern destinations up to Birmingham, with three ticket types (super off peak, off peak and anytime) being available and at slightly different fares to the NR machine.
Using a pink ticket issued to Birmingham Stations was fun after I'd changed to Cross Country and Virgin services at Banbury and Coventry respectively. Neither had seen such a ticket previously.
* = However, at stations where LUL provide the ticketing on behalf of London Overground (e.g. at Harrow & Wealdstone), the
TVMs▸ are actually LO's Scheidt & Bachmann machines and print on orange stock, just the machines are LUL branded. But the ticket office still uses LUL machines and prints on pink stock. Confused yet...?