If someone did 'create' their own BC they would have to know which seats were free. Which they couldn't do with any degree of certainty.
The system at the gate has its own way of monitoring heads.
No it is not 100% fool proof. Near impossible to exploit though.
The headcount never picked up folk on the wrong a/c that was picked up earlier with double booked seats when 2 people tried to sit in the same seat. The headcount only ever made sure that no one was left behind. The system now covers that.
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