Passenger full fare etickets are valid a year.
I've not read anything (either way) on
staff eticket validity, but can't imagine it's only
valid for the single day or flight.
The issue will be listing. You can't seem to
list on PSS without a new eticket. It would have
to be done by ground staff if you had your eticket
number.
Someone please correct me either way, but that's
my 2 pence.
Edit: just read post above and it sounds correct.
if you've got the eticket you should be able to 'go show'