Guild Wars 2

During August I managed to complete the achievement before the deadline.
The achievement reset completely as expected on the 1st of the month.
I then, within the past week completed it again and claimed my rewards.

Now with the reset of September’s achievement I am concerned about three things:
a) Having to do it again.
b) Claiming the rewards for it again.
c) If I do it again, is this an exploit?

I also collected the rewards for September and the achievement reset. Would be nice to know if there’s any point in doing it again