Anecdotally, I had a standby ticket recently when my seat was reassigned to a paying customer, although I still had a boarding pass for that seat. I was halfway down the jet bridge before the gate agent realized that my ticket had been revoked.
I imagine it's second nature for gate agents to let passengers through, and one lapse in judgement can cause the United incident, despite the software showing that the ticket was invalid.
Multiple human errors. Once she was on the plane, she found (unsurprisingly) that her seat was taken. A steward on the plane looked at her boarding pass and found her another seat.
I bought a gift card at IKEA in Shanghai for 100 yuan once. Shortly afterward, I visited IKEA in Palo Alto and asked a cashier how much was on the card. She scanned it and reported a hundred dollars. I asked her to confirm that, which she did, and then she offered me a "receipt" of the scan, which I accepted.
The printout correctly showed that the card contained 100 CNY. I've thought of IKEA ever since as a store where the cash registers are smarter than the cashiers.
I can't guarantee that it was usable -- I didn't try to buy anything with it, and for IKEA US to sell to me in CNY they'd have to have an exchange rate set up -- but it was definitely readable.
On the other hand, when I asked the recipient (it was a wedding gift) about it later, he reported that his wife had recorded it as having an appropriate-given-the-exchange-rate quantity of USD, so I suspect it was in fact usable.
Anecdotally, I had a standby ticket recently when my seat was reassigned to a paying customer, although I still had a boarding pass for that seat. I was halfway down the jet bridge before the gate agent realized that my ticket had been revoked.
I imagine it's second nature for gate agents to let passengers through, and one lapse in judgement can cause the United incident, despite the software showing that the ticket was invalid.