So there was been confussion on why it is now consider season 5.
Okay before I begin, let me explain what happened in the past,
1. 2007, iCarly was picked up a a series and in late 2007 the series went from 13 episodes to 25 episodes for the first season.
2. A second season was picked up for 45 episodes and went into production in April, 2008
3. For unknown reasons that season was split into 2 seasons
4. May 2010, the show got renwed for a 4th season, See blew what happened for Dan on production. (go to number 3.
5. the show was picked up for another season in 2011.
I am currently studing Television production codes and a certifred Television operator by the Society of Broadcast Engineers .
1. Production Codes are usually meaningless for the viewers, they are mainly used by the writters. The production codes can be useful in determining the writers' original intentions. Some "stand-alone" shows, such as iCarly may film episodes in radically different order to how they are aired, because character development and continuity are not major aspects of production. The airing order may in the end be decided by the network, based on ratings, sweeps months, or other network's competition.
2. Viewers Nomally will go by the Broadcast code. Broadcast code is the episode # with the season #. for instance, iThink they Kissed will have the Broadcast code as 301 becuase that is how it was broadcasted but still has the production code of 227 to match the script.
3. Nick ordered a season 4 with 26 episodes but Dan needed to split it up, so he could film Victorious. Dan still followed through with the orginial 26 episode order for season 4. He did however did not shoot 2 episodes because of Miranda's tour they were carried over to the next season.
So when Production season 4 started airing Nick promoted it as a new season. Sometimes networks do that to try to attrack more viewers for the show. In this case it was still one season.