@Mauricio *****
You snuck in your comment right before I close, so I'll respond to it.
The extension of stay is the responsibility of the passport holder to confirm that the date is correct. *IF* someone was supposed to get a 30 day extension of stay, and he got one year by mistake, it does not mean he can stay in the country for one year - after the 30 days are over, he'll be on overstay.