A lot of people on this wiki believe that episodes 402-409 are part of season 4, while others such as me say they're part of Season 5, as nickelodeon advertised. In a similar scenario, I for one believe episodes 501-509 are a part of season 6, according to Wikipedia. Where do you stand on the whole 4 vs 5 vs 6 debate?
Here's Where I stand
Season 4: iGot a Hot Room -- iParty with Victorious
Season 5: iLost My Mind -- iToe Fat Cakes
Season 6: since iApril Fools