Cakes will continue to produce until they are spent. I have noticed potency dropping after the second flush, may just be my experience. I usually let my bulk grows go for 3.
Later flushes on cakes have produced fewer though larger fruits ime
βWhat goes on inside is just too fast and huge and all interconnected for words to do more than barely sketch the outlines of at most one tiny little part of it at any given instant.β - David Foster Wallace