I used to wonder how nessecary it was for cc to check ticket stubs when boarding the aircraft, given paxwill have had them checked only moments ago by the ground staff. I got my answer about a year ago when I was waiting my flight to depart for Edinburgh, when the cc at the front informed a boarding pax that their ticket was for Glasgow! Responsibility for pax and ground staff there I think.
A little off topic, but I was boarding a recent flight (BHX-EDI) when it was announced by ground staff that the the BHX-EDI and BHX-GLS flights were being combined (they have a track record of doing this) and therefore seating allocations were null and void and seating was 'free'. It somewhat caused further confusion when boarding pax asked the cc (and I really don't know why they felt the need to ask, having been given explicit guidance from the ground staff) if it was 'free' seating. As the cc responded saying that pax had to take their seats, which stopped working when the different flight seating conflicts started to become apparent.