Jane's has missed so much and me too, I am disappointed but ... and in fact that was one of the reasons for me to quit since they have a very special own way of taking something for "confirmed". I remember back then when the WZ-7 was seen for the first time with a serial number and I wrote in my report that it is assigned to the 16th Air Division, 48th Air Regiment since it carries a 21x7x serial numbers.
They replied, I could not be sure even more since there is no 48th AR active according to their own data-base ... my reply, that's in fact the news about it since 21x7x confirms the 48th as re-established was again turned down since they could use only something as confirmed when it fits their database.
Anyway, I spoke to the Satellite imagery guy working for Jane's and he explained me that in contrast to me, who uses a combination of factors to calculate such numbers, they just take the highest number of aircraft spotted at a certain time on a certain base.
So in case for the 4th AB at Foshan, they maybe count only 6 since only 6 are visible, whereas I look the the serial numbers and see the highest one confirmed for the 4th AB is 61252 aka 22, so per my calculation, Foshan has already at least 22 J-20.