People who do restoration work make reproductions of parts and assemblies all the time. It is an advanced form of repair work. People who buy top shelf restored items can expect as little as 10% original. In addition racers have used TONS of custom items in racing and brands buy "specials" they are unable to produce in-house all the time. I am really surprised more of it does not turn up. I don't know at what point it becomes fraud however. I think both those mentioned would be fraud as they are trying to go up-market it seems.
I guess if someone thought they were buying a $50.00 vintage raleigh MTB and found it to be a $3,000 Ti prototype full of works parts it would not be too bad.