In wondering about what happens with shared barriers, ambiguous
platform readers etc, I looked up fares from Greenwich and Lewisham,
both boundary zone 2/3, to Euston LU (random zone 1) on the TfL Fare
Finder.

It seems at a glance that it's cheaper from Greenwich than from
Lewisham, but the same from Greenwich as from Lewisham DLR.

(Unlike some, Greenwich doesn't offer separate DLR and NR options in
the drop-down, presumably because of a shared entrance. Are any of
the readers dedicated, eg the one on the DLR platform that's also the
NR platform?)

I also note that it's more expensive from Deptford to Euston than
Greenwich to Euston.

Could it be that DLR is assumed? If you click on "plan this journey"
it tells you to go via London Bridge NR, with no warning about fares.

If you click on the button to check if there are CHEAPER fares/routes,
it then offers via London Bridge NR (and other NR) as being at the
same price as from Lewisham or Deptford, ie more EXPENSIVE.

So, presumably in practice you'd be told the DLR fare, with no warning
that there's a more expensive fare, and be advised to travel via
London Bridge, and then find yourself deducted the higher fare?