Tristan Miller wrote:

Is it permitted to travel between Liverpool Street and Maryland with a
Zone
1-3 Oyster travelcard? There's no Oyster card reader to touch in or out
at
Maryland, though I've made the journey both ways several times without
apparent incident. That is, going from Maryland to Liverpool Street, the
exit gates have always opened upon swiping my card, and going either way,
I've never had any money deducted from my PAYG balance.

If I were to encounter a ticket inspector at Maryland, would I be in
trouble for not possessing a valid ticket?

No problem at all. I've done exactly the same from Forest Gate for years
now.