I've had the same thing with points. Pulling up the reservation sometimes sticks, sometimes not. Never hurts to have a printout. I have found, though, that the conductors have a pretty good list of expected passengers and can put you in with no paperwork at all.
I still remember leaving the house for a train trip and leaving the *tickets* at the house. There was a frantic cab ride to the house and back.
Even further back, I was planning a trip from San Francisco/Emeryville to Reno and back in a room. There was a "travel agency" that said they would send me a book of gambling freebees if I booked through them. They sent me the booklet, but no tickets. I was frantic to get my hands on the tickets, so finally went to an Amtrak ticket office. They were able to cancel and rebook the ride at the same fare and print my tickets. I found the tickets in my mailbox when I returned from the trip. When I contacted the travel agency to complain, they said, "We send the tickets out at the last minute because people often change their plans".