Well, I must admit, I do not fully agree and even if more than clear - even to me
- both programs are running on different schedules and are barely comparable in terms of timeline, a comparison "just for fun" is anyway interesting since I indeed expected for such an important program a faster progress:
Anyway, if correct, this is actually the third known prototype even if I won't be surprised if there are already more out ... overall I expect a similar number of prototypes - in fact even more since SAC must expect losses during the trials - if not more than for the J-20 program, where CAC had altogether 6 true prototypes. So if we try to compare both programs and equal the J-20 demonstrators 2001 & 2002 to the FC-31 demonstrators V1 & V2 aka 31001 & 31003, then we could rate the first true program milestone for both the maiden flights of the individual prototypes, namely the first true prototype no. 2011 is comparable to the first J-35 prototype no. 350001 and all subsequent prototypes and so on.
Again, both programs are barely comparable since we do not know the PLAN's schedule, nor the budget, nor anything else and as you always remind me: SAC is different to CAC, namely much more secretive.
J-20:
no. 2011 - March 2014
no. 2012 - July 2014
no. 2013 - November 2014
no. 2015 - December 2014
no. 2016 - September 2015
no. 2017 - November 2015 = 6 prototypes within 20 months ---> service entry December 2016
J-35:
no. 35001 - October 2021
no. 35003 - July 2022 (?)
no. 35005 (?) - September 2023 = so far 3 prototypes within 24 months
Anyway, it will be excieting to see, what's next!