It is completely unacceptable to have that much of a lapse of time between drills. The U.S. Coast Guard would not allow it, but then the Concordia was sailing in Europe where local regulations appear to be taken as suggestions, such as traffic lights in Napoli.
All newly embarked passengers on a cruise such at that one should have to attend a briefing prior to the ship leaving the port.
A larger issue appears to be the communication breakdown between the crew and the many nationalities aboard as passengers. That one is a tough nut to crack.