You haven't watched the show then. Anyone who hasn't entered Lyoko, doesn't remember anything during time jumps. Jeremy remembers, because he has, in fact, entered Lyoko.

The only time that rule is broken, is in season 4,
[hider=spoiler]
when the new character
[hider=Even more spoilage, yada yada yada]
mess with the super computer
[/hider]
to not forget.[/hider]