You should anneal longer each time a piece is fired.
It seems the idea is that each time you do something to a piece the risk of poor annealing increases. So, an increase in annealing soak will reduce that risk.
In fact, you should anneal for the thickness of the piece plus any additional complicating factors introduced. No further annealing based purely on the number of times fired is required.
If you have merely added a layer of powder to the glass, you only need to anneal for the thickness of the base. It is when you begin to add significant amounts of frit or other glass pieces that you need to increase the annealing soak and also slow down the annealing cool. If you go on to complicate matters by only tacking those elements to the base glass, you will need to slow down even more. This blog post gives some indicators on how much you need increase the soak and slow the cool.