In article , Robert Woolley
writes
Allegedly a maximum cost single will be deducted and then some
credit will be put back on at the end of your journey.

Correct.

If you only validate on exit, the full cost comes off.

The full cost of what? Are you implying it would be the most expensive
fare that you could have needed to get there (eg a single from Z5 if you
were exiting in Z1)? Is there any warning in case it was an equipment
fault that prevented the registration of the start of your journey?
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