Wiki is a poor source. At best a cheat. WZ if I remember correctly is the proper for an Engine of Chinese make but not the attack chopper, that properly should be Z10.
Still no unit numbers. Is this a production plane or another prototype ? The stealth on the Z-20 must be better than on the J-20 since we don't see it as often!
I'd say most chances are Z-20 is in testing phase still. It may have finished most of development and some pre-serial batches may have been made and various airframes are serving with PLA, being tested. But perhaps not all feedback from the testing has been implemented yet and full scale serial production hasn't started yet.
Interesting comparison of the Z-20 prototypes no. 632 and 636: Slowly the images are getting better and better ... can't wait to see the first Z-20 in full PLA LH serials