Barry Salter wrote:

It's also worth noting that there are Oyster validators on the Central
Line platforms at Stratford (or at least there were last time I went
through), so you might want to touch in there as well, just to be on the
safe side.

However some mainline services depart from platforms 9 & 10, especially on
Sundays when the fast and stopping services get mixed up.

Also if you're travelling onwards on a paper National Rail fare on either
the North London Line or National Rail then the Jubilee barriers are the
last you've come through. Just how does the system know that you've finished
your Oyster journey?