No, they don't.
That is only a number on the bottle. It is a rough estimation of the final grit level, with a lot of average use: avg. pressure, avg. amount of polish, average time of the spinner, etc.
I know a friend who used a "dose" of Step#2 and got the rough equivalent a 3000 grit high gloss shine, because he pressed and pressed and use a bunch of the polish.
Those numbers are not fixed. It's not a magic number. You don't automatically get a "15000 grit polished" surface by magic. The abrasive inside breaks down finer and finer as you press harder and harder. The finer the abrasive, the higher the grit number and finer the resulting surface.
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"None are so blind as those who will not see."