Re: "So & So" Motorbikes, I don't get it???
Going back to the manufacturer/assembler argument. Across pre 1939 Europe, most small "manufacturers" used bought in components. They may have had to stamp out some plate, or send out for castings occasionally, but they mostly bolted bits together.
This thing about buying bits in and putting a name on then is nothing new. All you have to do really, as a buyer of a complete machine, is to look for the name with the best reputation. The rest of us have to go out looking for unreliability.