Seeing that the ball you polished worked, says you most likely have been using too much surface on your balls for the conditions your on.

Instead of just using 500-1500 grits try some 2000, 3000, 4000 grits also and add polish if needed.

Rarely do I ever use more than light pressure when sanding.  Our spinner also has a water supply, which helps a ton.  Water acts as a "lubricant" and can help you fine tune reaction, along with speed and directional changes. 

As you practice you will find what works best for you.  Good luck.

https://www.youtube.com/watch?v=khUITPlM5-Y
Always thought grit adjustment worked like this. I understand about burnout but never quite understood how going to a higher grit could increase hook. Will give a higher grit a try.

Yes with reactives you are changing where it hooks with surface adjustments (though you can reduce hook if you push the breakpoint far enough down the lane it doesn't have time to hook).  With urethane you are actually reducing the hook going with higher grits.

Resurfacing equipment represents the most customization you will find in bowling.  In my opinion, even more so than drilling.

To answer your first question, yes, the multiple grit numbers listed usually represent the final two grits used.  Some are small differences like 500-2000, but some have been more dramatic like 500-4000 that was used on the original Virtual Gravity. 

When you see a single grit number, this usually means the final measured grit is that number.  So if it says 4000 grit, then it should be 4000 grit when measured with a scanner.

All said though, it doesn't mean much.  Even in the factories, there are differences ball-to-ball.  Pads age and deteriorate meaning the first ball a pad sees will be different than the last ball.  You can open two boxes with the same ball and they may not read the same surface or even look the same.

So, what this means for you is do what works for you.  After I purchased my spinner, I spent a lot of time experimenting what works for me and what doesn't.  How much pressure, how long per side, which pads to use, how many uses per pad, which polish is best for me, etc....  And you will, or should, do the same.

As a starting point, look at these charts to get an idea of the variations and their effects:

http://wiki.bowlingchat.net/wiki/images/5/57/Bowling_grit_chart_v2.pdf

http://wiki.bowlingchat.net/wiki/images/0/02/BJI_Surface_Chart.pdf

You will hear how bowler x likes one grit while bowler y likes another.  Doesn't make either one right or wrong, but it also doesn't mean it is guaranteed to work for you either.