There is a 99.9% conviction rate in crimes in China [2] (which is the same as basically having no rule of law) and political prisoners seemingly 'disappear' all the time.
China are known for lying consistently about almost everything and keep a tight lid (as much as they can) on anything that would cause them to 'lose face' both within and without the country so any estimates are likely significantly low.
[0]:https://en.wikipedia.org/wiki/Organ_harvesting_from_Falun_Go... [1]:https://en.wikipedia.org/wiki/Xinjiang_re-education_camps [2]:https://qz.com/246696/chinas-criminal-conviction-rate-is-99-...