I'm not familiar with DK3 - does the score roll at 1,000,000?
Without someone de-compiling the code is it possible to know if the 30,000 bonus lives cut out or if it was a programming "error" with the original programmers not ever assuming a score would go over 1,000,000?
My favorite game is Bump 'n Jump - this game gives bonus lives every 30,000 up to the rollover. The game rolls at 1,000,000, meaning the last bonus is achievable at 990,000. This game also neglects to give the 990,000 bonus life if your score goes from say 970,000 to over 1,000,000 (getting the 50k bonus at the end of a level). I.e. you must have a score on screen between 990,000 and 999,998 to get your last bonus life.
This is what makes me think for this game at least, that it is something to do with the score rollover and a programming "error/lack of foresight) that causes it to stop.
Much in the same way DK killscreens on 22-1, I highly doubt a lot of the stuff that happens in the particularly older CAG is in there on purpose, but because the original developers never reckoned with the skill and determination of the people playing the games.
Sorry, that was slightly off topic