Recycling old memory chips has been a trade for China's brands for a while. Not just GPU memory but also others like RAM, and NAND flash memory,...
With the massive semi conductor chip shortage such business practices are expected and not ending any time soon , but not were such is done and sold as brand new instead of refurbished is dishonest trading, probably stealing to a large extent!
You may not know, but some China NVMe SSD also uses shitty or low-yield NAND or even recycled NAND from used SSDs. The same for some questionable Chinese RAM brands like Kingfast or Kingspec (copycat of Kingston name).
Dead VGA cards with untouched VRAM could still fetch a good price even if it not working or are completely dead (ten bucks for RX 470/570 model with 8GB last I check).
Several youtube computer geeks like "linus tech tips "have done speed tests and teardown to see what these GPUs, SSDs are made of and what you said was true as they are mostly knockoffs with a 50/50 chance of working .
To be honest, it was very eco to make use of everything even the old and busted memory of all kinds. Still, advertising it as a brand-new product is dishonest. My advice: don't take anything from China's market at the face value, check reviews from many other customers or broke-down, disassemble reviews like OP mentioned.
People who are privileged to know this information know what to look out for, but who will tell & protect the first time buyers with no knowledge of these refurbishing practices of chip's and what not...