Originally Posted by number_6
I actually flew on the last day + 1 of validity once, but that was due to a schedule change that took the last flight past midnight. Luckily I was protected as it was for dated tickets and they didn't make me fly 24 hours earlier. Every agent noticed the ticket validity date, though, and commented upon it, so they do look closely.
On the other side of 'look closely', one time when BA reissued for me the agent mistakenly used the original ticket sale date + one year for the "'valid until' date. As that date was well before the last scheduled flights I was ready to be challenged and have to argue the rules - on my particular coupons, that date was printed in bold 72-point font, raised red letters, and somehow seemed to be illuminated by a little spotlight - but no one mentioned it. (A plus for having reservations in the computer, I suppose.)