[TeMPOraL]

Depends on an airline and maybe even airport, I guess.

Anecdotally, last time I was flying on a business to Germany with Lufthansa, my cow-orker did the Internet check-in for me without me knowing, and printed out the boarding passes. I later did the check-in for myself again, and picked a different seat. At the airport, the friend gave me the boarding pass he printed (with the old seat number), and so I thought, let's check if it still works on the scanners. I scanned it when boarding, and the scanner threw up an error that the seat on the pass does not agree with the one that's actually booked. I pulled the up-to-date boardin pass on my phone and continued on my way - but it seems that there is some actual checking being done, not just CRC.