Two years ago did a 14 sector round the world trip. Had to carry paper vouchers for some land side trips to hand to the guides but carried just one piece of paper for all the air travel which listed ticket locator numbers. This worked fine at all the check ins with Aer Lingus, Virgin, Singapore, Qantas and Air New Zealand and a couple of immigration checks, when asked for a ticket, until we got to the Cook Islands.
The woman on immigration wanted to see a paper ticket, had no idea what a locator number was and made out that the list and the stamps in my passport from previous sectors meant nothing. As far as she was concerned, my wife and I were potential economic migrants! Eventually, to save holding up the hundred or so people behind us in the sweltering customs area, she called someone from Air New Zealand who quickly put her right.