OK thanks for the replies so far. To give you a little more detail without identifying the flight I will say it was a the second sector for the crew and the total 9including turn round) was 8hrs so whilst I appreciate how tiring the work load can be it could not be put down to fatigue. There was also an announcement to say where the aircraft was going and anyone NOT going there should disembark immediately!
I understand the ground staff were at fault but it is not the ground staff who are responsible for the aircraft. Of course it would be found on head counts etc if the flight had been half empty and whilst I sympathise with the CC they very clearly were not checking people on board properly. This applied to both front and rear embarkation.
Is there likely to be a change of procedures/training etc attached to this or will the company be unaware unless there is a complaint made? Should this be reported to the company without identifying the flight so that awareness is highlighted?