Hi

If anyone could help me figure this out, it'd be much appreciated...

I have a monthly zones 1&2 travelcard on Oyster. However, a couple of
mornings a week in future I will be travelling into central London
(Victoria) from Beckenham Junction (zone 4). The train I'll be getting
calls at Herne Hill (zone 2/3). Does this mean I can just get a single
from Beckenham Junction to Herne Hill, and my oyster travelcard will
cover the rest of the journey? That would seem logical to me, but I'm
not sure what would happen at Victoria, as I wouldn't be able to
"touch out" to get through the barriers as I wouldn't have "touched
in" at any point.

Any ideas?
Thanks
Jenn