I did eventually solve the problem JB, although it took a fair bit of detective work. I was determined to find the answer because it was really annoying me, so I found one of the original game developers on linkedin. The message exchange is as follows:
thanks for accepting my invitation, and here's hoping you don't mind my asking a question about something you helped to create way back in the 80s.
I was a big fan of 3D Galax when I was younger, and I've recently re-discovered it on an emulator.
But could you help me with level 99? I've managed to kill some of the enemies, and I can see the rest of them on the radar at the bottom, but they always seem to be at the wrong latitude. Occasionally I see one or two in my viewscreen, but I can't move up and down far enough.
Any advice you can give me would be much appreciated. After almost 30 years of playing it, I am determined to finish it one day!
Thanks in advance
ahhh ...... ummm..... Blame [the other developer] for that.
I think the advertising he sent out bragged about over a 100 levels, but when we came to ship we could only get 99 levels in.
He wouldn't give me the time to fix the problem because we had already paid for the advertising and had to ship at the same time as the advertising came out.
So I made level 99 impossible.
Not an ideal solution, but the only one I had available to me at the time.
Ian did this to other projects as well, sorry man.
So if you got to level 99 then you have effectively finished the game.