Miyata is Japanese as you know. Koga is Dutch. In 1974 Andries Gaastra (which was employed at Batavus) did start his own bicycle company with his wife Marion Kowalik. Girst letters of noth names became KOGA. Frames came from japan, and were completed in Holland. They also intoduced Shimano to the Dutch market.
Jan Janssen 1976 (caballero 1970 team replica)
Koga Miyata Gents Racer S1980 (in use by my son)
Giant Peloton Superlite 1998-2002
Diamant cyclocross late 80's
Favorit Czech 1978