Thanks Killer Gorilla! Here's my reply from the Lemon Amiga forum:
Those are extra levels indeed, not included in the standard range of levels. Judging by the level name "Ode to Christine" I'm sure about that, because Christine was a girlfriend of the guy I mentioned.
In the mean time I've got some good news: I contacted the guy and he thinks he's still got the extra level packs. Must be around 100 he said. Thanks for your research!