Hi Luca P.,
You do not tell us if the count was done at the end- a final table chip count, or if it was done while the event was still under way.
If at the end: I would be very concerned that large denomination chips have been pocketed with intent to use in future events.
If counted by the players: It is nearly impossible to get an accurate count- it is why we stopped trying to verify chips as we bag them at days end for multi-day tournaments.
As Stuart points out, the chip race is a likely source of counting errors. Every effort should be made to have a dealer, supervisor and one other person/player witness the color up to assure accuracy.