[we really don’t know a whole lot about the extent of China’s blue-water navy.]
They’re impossible to hide. Satellites pass overhead and take snapshots. Orions and Poseidons are always watching. We don’t know the number of Chinese nukes with any certainty, but ship counts are probably not an issue, since they have to be operated out on open water for the crews to get familiarized with maneuvering and working the various weapons systems while at sea. Not to mention learn how to handle peacetime encounters with foreign navies.