Well not known does not mean not exist. I really don't know why people are so shocked at the possibility of over 60 J-20s at this point ... after all we have not seen even a single operational Taihang J-20 even though they've been produced since late 2018. More likely than not, the PLAAF has deliberately increased censorship of the serials or even photographs. So we are truly in the dark when it comes to the numbers.
Not shocked, but highly sceptical and that's the point.
On the one side we have some reliable reports from some big-shrimps suggesting about "60 until year's end", which is eagerly picked up by some - one forgives me - "fan-boys" as "60 per year", which means 60 in 2018, 2019 and 2020 and as such more than 200. But let us take a look if 60 are possible or realistic.
On the other side - and I'm well aware to ruin the party again - there are those with the minimalist approach accepting only confirmed units and confirmed aircraft numbers.
So as such let me try to put both arguments side by side in the meaning that the truth lies most likely somewhere between the 60 altogether and the about 20 "confirmed".
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60 per year is highly unlikely (IMO plain impossible) given any so far seen comparable production rate of J-10s, J-11/15/16s. It also does not fit to any other confirmed point and that's the issue:
We know so far exactly 18 J-20s confirmed by individual numbers, we know production of the WS-10C-powered ones started at around mid-2019. Since then we've seen "several" yellow painted ones at CAC ... but: these "several" are altogether only a hand full of images with a maximum of 4 in a shelter together. As such assuming 60 per year - which would equal a rate of 5/month - we must have seen more, we must have seen more delivered to operational units and most of all we must have hear anything on a new Brigade besides the three known ones. Not even Anshan is confirmed even if we have reports since late 2019/early 2020. And I cannot think that all three units at Dingxin, Cangzhou and Wuhu are using 20 each since no satellite image so far shows so many.
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60 altogether is likely but even here I'm sceptical due to one major argument: namely we have not even rumours on additional units. 60 altogether would fit to my assumption of about 8 each at Dingxin and Cangzhou and maybe 12-16 (aka 2 daduis) at Wuhu. These would be about 32 in the first 3 units and about 28 or exactly one additional brigade - at an so far unknown unit. Again so far there are no rumours of a new unit besides Anshan (1st Brigade) and I'm at least confident that such a high number of J-20s would have been spotted.
Therefore in conclusion I find 60 not unrealistic, but unlikely and my guess would be around 32 aircraft by now and maybe 40 altogether by year's end.
Otherwise I urge all supporters of "there are 60 or even more" to explain, where these missing birds should be?!