Please don't get upset I am reading your replies, I am just trying to explain why I don't think what you are saying will work and in this I have been quite humble in saying that hey that might be my fault. I do appreciate the time and effort you are putting into replying.
But to respond: previous score is not the score when a life was last awarded
So:
Every time any points are scored (1, 10, 20 etc..) it calls addScore( points )
Which does
prevScore = global.score
global.score += points
if(the offending condition):
awardExtralife
That is called every time 'any' points are awarded, so prevScore tracks one point award behind global.score
So the check is to track a score as it increases and add an extra life everytime it goes over a factor of global.extraLifeEvery (100, 200, 300, 400 etc.)
If that doesn't make any more sense then please don't get stressed over it. The problem is solved and the actual routine improved so all is good.