I think ideally we'd like a pictures of a J-20 with unit numbers corresponding to the 99th for that.
The idea of additional J-20s being transferred to WTC is entirely reasonable, but whether it's for 99th specifically, who knows.
Exactly!
There is too much speculation at the moment since indeed there should be at least 3-4 new units under conversion or already flying older J-20s including those older AL-31FN/FM-powered ones from the 9th since the 1st, 5th, 9th and 41st are now confirmed to have received J-20A, but we simply don't know enough!
My guess would be, those from the 9th went to the 177th and those allegedly for the 43rd are from one of the other ones mentioned above.