If it was a convo with the silver haired ticket clerk, I remember having a similar chat with him about it. There's also a chap with glasses who's cheery.

Regarding the rail travel vouchers from other train companies, as long as it's issued in the correct manner, they're obliged to accept them. They can also be redeemed for Travelcards on Oyster in addition to PAYG.

At one time, you could also redeem them at London Underground ticket offices, but they've stopped doing that since the ticket office closures started.