I would take the gasket and diaphragm out of the working carby after wetting the gasket with fuel or CRC so it doesn't rip then try the working gasket and diaphragm in the carbs that are flooding that will at least tell you it's definitely the new spare parts are the problem .
It doesn't sound like any of the carbs that are over fueling are missing the brass jet as you have 4 out of 4 over fueling.
When I was around 14 ,I would help my next door neighbours brother out doing deliveries to many Factories which I got paid for and it was quite common for the Factories to have manufactured seconds in the skips, we would take new parts out of the bins when the parts were at the top and it was always interesting to see what went wrong with the parts.
The problem is people that work at some Factories take new seconds (rejects) out of the bins and sell at markets and eBay. This doesn't happen much in Australia because factories lock their bins an have a surveillance camera on the bins as they don't want rejects being sold and people will say their products are faulty.
I find the selling of seconds from China is quite common these days from markets and eBay.
