My working assumption is that Miura and Epon (Endo’s brand name) forged heads are Japanese forged. They are not always assembled in Japan. They do sell just heads and are assembled by builders everywhere, including the U.S.
Endo has a plant in Thailand. Not sure what the split is between Japan & Thailand.
Miura’s Passing Point Neo Genesis line is made in China & inspected in Japan.
Sorry, I meant Miura’s one piece forgings. Neo Genesis is a two piece club. The face is an insert. I try to avoid Chinese forging unless certain circumstances, siuch as the OEM owns the forging house or the house is known and expected. China is a huge country and some manufacturers make excellent heads and some are really no better than counterfeit clubs the tolerances are so loose.
Thailand I don’t know much about golf-wise. Taiwan manufacturing is well-regarded in many fields, such as steel bicycle frames, which are outstanding in my epxerience. The challenge is China can be great or awful, and it can be difficult for consumers to know.
I thought all Miura’s are two piece - spin welded necks.
I think you are correct on that point - there are videos of the Miura & MG models having the hosel spin welded. I think are only a handful of brands that make fully single piece clubs, and then you get brands milling from single blocks of forged steel for their irons eg Seven Golf.
I even think my Seven putter is from a single block, beautiful milling in the neck and face.