In sweden attendance is based on people passing to the gates = fans attending the game, not sold tickets. I am pretty sure that Man United announced less attendance at one of the games at Old Trafford last season that what they had announced as "tickets sold" before the game start, but I could be wrong. It would be good if I could check that up though, so I dont spread misinformation :-)
But its stupid to announce sold tickets as attendance especially when you have the big games at arenas where the clubs have given away free tickets to team, schools, sponsors that fail to show. I am sure that was even more of an issue when clubs started with womens teams on big stadiums. I do remember Arsenal playing at the emirates once where you could question if it was 10 000 - 20 000 less fans in the seats than attendance announced just based on the eye test.