thank you for your post and question.
In previous versions of fuzzylite (4.0, I think), the defuzzification was computed when
defuzzify() was called. This behaviour changed in (5.0, I think) so now defuzzify computes the defuzzification as stores it as a value. Hence,
defuzzify() computes defuzzification, returns void, and you can access the defuzzified value using
Hope this answers your question, else please feel free to post again.