Actually, a while back I found some screenshots of what some of the hell levels used to look like when it initially came out, which makes me think they weren't tested at all
54.12.1G.0 Notice that if an apricot dies on the left side of the screen, the mini apricots will be impossible to kill.
54.8 Okay, this one was possible, but it was even harder than it is now....
The other screenshots don't seem to be there anymore, so no link, but...
54.4: the 1 square platform at the top didn't use to be there, making it impossible without the book of stars if you didn't kill the top left pear as you came in.
54.6 and 54.12.1.7 used to have no black bombs, meaning killing the last enemy was impossible.
Lets not forget that level in the tomb which is impossible without losing a life without

, which still hasn't been fixed.
As a side note, I also found an awesome screenshot showing the locations of all the spikes on
54.9Finally, I can also confirm all levels are possible without the book of stars. There is a video out there of someone getting to the real tomb of tuber without the book of stars, but the video ends there, so I don't know if he has the red bomb.