The trick is to always assume "China is lying about its internal statistics" and inflate whatever number they give by an arbitrary large percentage. 1.7M is obviously an under-count because the CCP is always lying about everything.
Also, you can do some broad brush "Everyone in Tibet, Xinjiang, Hong Kong, North Korea, and Taiwan are prisoners of the Chinese state, so actually that's over 60M people" napkin math to make the numbers look better.