I'm not 100% clear, but I have always thought of the rankings as a kind of waiting list. If you were not an exempt player at the start of the year, you are waiting or qualifying. Take me for example, I missed the last tournament so I'm no longer in the top 32 but I'm still exempt. Even if I fall way down in the rankings, I still get a spot.
When they changed to exempt instead of touring pro we were given a timeline that we were exempt from needing to qualify. I believe the top 32 get 2 years of guaranteed spots and 32-40 got one year.
That is the way I interpret things, I could be totally wrong.
Sarah