I think J-21 was in competition with J-20 but lost out, so they adapted it to become the J-31 for export and also to see if the PLAN/PLANAF would be interested. I don't think they use J-21 term anymore.
HK need to know among other things that their citizens continue to have a high standard of life after the british left are partly due to some of CCP's policies. They are being subsidised at the cost of poorer mainland Chinese (Yet it is the poorer mainlanders that are looked down upon). HK would...