This was just a continuity error. Happens in movies all the time. I'm sure George would have liked to have remembered the line correctly in which case Palpatine would've said "generations". From an in universe POV, I'm inclined to think that Palpatine just made a simple human error & slip of the tongue. Not a big deal. I'm sure GL would have a laugh that a minor continuity error has sent so many fans into a debate.