Post by snoggle on Mar 9, 2013 13:21:30 GMT
A complete guess but as an Oyster card has three "slots" for season tickets perhaps an old one will simply sit in a slot until such time as subsequent ticket renewals use up the slots and then "push it out of its slot". The system clearly checks each slot to see if a ticket valid for "today" is present and if an old expired ticket is in a slot it will ignore it for the purposes of travel. However a check of the card will still show it there. As I say - a guess. It would be nice if someone with more knowledge could confirm what does happen.
