Season 4 ended with Episode 52, and season 5 starts with Episode 92, leaving a gap of 39 episodes to emphasize how much time has passed.
At the end of the closing credits, the Cartoon Network logo (2001-4) gets sliced by Jack.
For the last season (2017), the Cartoon Network logo opens up to show a shot of bearded Jack.
The episodes are listed as Roman numerals (I, II, III, IV, V, etc).