Elements that were either retconned in later seasons or cut out/forgotten altogether

[TMC]

• Josh writing for the school newspaper.
  
• Drake playing a cherry red Strat and having a female friend as a bassist in his band (they are all boys later on).
  
• Drake not having a driver's license and continually failing his test (he is driving around legally in Season 3 without any mention of him passing his test).
  
• Josh's penchant for video gaming and talent in billiards; 'Crazy' Steve losing his job at the theatre Josh works at (they are co-workers in Season 3).
  
• Appearances from Josh's 'Grammy' played by Randee Heller (though she is occasionally mentioned in later episodes).
  
• Drake & Josh's juvenile criminal record from selling stolen goods unknowingly as teens (in a TV movie some five years later, they are charged again as adults and given a farcical criminal trial, and no mention is made of these previous offenses).
  
• The boys' little sister Megan keeping dangerous pet snakes in her room which terrify them (in Season 3, she instead has a beloved hamster named Herve and also a sheep she "bought off the Internet").