The precursor chemicals have legitimate applications and everything the PRC approves of exporting and manufacture is accounted for. Someone is doing shady corrupt stuff on the US side of the pacific and laundering it through legitimate concerns such as medical labs. The CPC controls the outputs of the chemicals very carefully and stringently, who knows if there is a black market but there’s definitely more of a problem on one side than the other in both supply and demand.
There is definitely a grey market and not just for precursors. A lot of research chems (specifically in the sense of novel drugs that aren’t illegal in the US or elsewhere because they’re new) come straight from China. There are other extremely potent opiods that SWIM (yeah I’m using that ironically) can only get from China, like metonitazene, etazene, or less potent like 2map237. Been told that the producers in China are given a green light as long as they only export. If they start selling these chems in China, they will be dealt with as harshly as someone selling H, but officials look the other way as long as it’s bringing money into China and only sending the dangerous chems out of it. I have no idea if that last part is true or just more anti-China nonsense. But I do know those chems are shipped directly from China and they are not just precursors but can be used right out of the box.