If you transfer on the Tram you don't get double charged.

That isn't quite the whole story. It only happens because a second tram or
feeder bus journey within seventy minutes of the first validation is free.
If you are already on the second journey and the tram is cut short then you
are charged when you touch in again on the tramstop (as you are required
to).

In fact I used to escort my grandson to school from Elmers End to Mitcham
and coming straight back meant I only paid for a single!

However if one of those tram journeys had been cut short you would have been
charged for another journey when you touched in again when you are really
entitled to another free journey.

I think that you should be allowed unlimited tram journeys within the
seventy minutes and not just two as it would solve the problem of trams
going out of service at a stroke.

So clearly the technology is available.

Indeed and it should be implemented a lot wider.

It doesn't seem quite fair that the T31, T32, T33, 130 and 314 buses are
given a privileged status when it comes to combining journeys with the trams
when plenty of other bus routes are used to connect with the trams, and
indeed they can be carrying passengers from a lot further away from the tram
stops than those in the New Addington area. There really ought to be a roll
out to every single bus route serving tram stops for starters.