Concur - but even having paper copies won't help if the e-ticket number has changed and you are unaware.

Somehow our joint booking got split on a (001- stock) LONE4 when flying ORD-FCO. Routing,everything else was the same - just a new booking.

I notice this before leaving Rome and took down my new PNR, SWMBO's was the original. That was where I erred - I should have looked for and recorded any new ticket numbers/PNR's as well.

On checking in with IB to fly to MAD, they could not find my ticket number and the new SABRE PNR was not useful to them to look up. They needed the Amadeus PNR which I did not have on me that would have led to the ticket number . I had printouts of lots of things except any containing the new ticket number. They would not let me check in without it.

I had no internet access either so could not look it up online. ¾ Hour later a call to the FCO AAgent (they were only open in the morning for the departure that day) managed to provide it - from there I was able to check-in and get BP's issued etc.

It was a nervous wait indeed and it was fortunate I like to get to airports 2 hours before anticipated boarding (not departure).

When I had time later, it was easy enough to get my new ticket number online.

So, yes, in all cases, it is best never to check-in without all relevant PNR's and ticket numbers, if you observe a change (such as split bookings) this is even more important.

(FWIW, having split bookings was an absolute PITA with seat allocation etc for the remainder of our travel on that LONE4.)