I agree, if you melted down old pistons to make new pistons it would be a piston alloy. If you melted down old cylinder heads to make new cylinder heads you would have a suitable alloy for cylinder heads and if you melted down a gold wedding ring to make a new ring it would still be a gold ring. It's plain logic.It would be true to say if you used clean cast iron from sleeves and engine castings and the like it could produce a good product. But if you use those curved seat pieces or exhaust manifolds that are burnt out and rusty and old building decorations etc you might get any quality. Cast iron was a wonder material back in the day and they had expertise to get a good product that was used even for bridges. Old cast iron machinery lasted for 100 years. Now we could be even better if we tried but those guys might not always have the good information. After all Honda himself started out making CI rings for rebuilding the little motors after WW2 but they were shit quality and did not last. However he went to college to find out how to do it properly and worked his business up from there.
Jaahn