For the lifetime of the plugin ?
The conversion rate applies weather its 10 days old or 10,000 days old.
So kind of irrelevant statement.
Using your math
Purchases / Uniques x 100 its a conversion rate.
So either you have limited uniques and high sales or pro rata..
Conversion rate is jut a % but is very significant, 6% seems extraordinarily high based on just under 1500 sales, perhaps you get lesser uniques..which results in higher gain...i dont know, either way it is miles above others i would guess.
Most direct sales companies work on 40% min. But thats a different beast