One aspect of the low countries is that they aren't nearly as chauvinistic as, for example, the French and the Italians. (Not an opinion, merely an observation.) Also, and maybe as a result, they didn't have much of a local bike parts industry, even though they are true cycling countries.
Many Belgian and Dutch bikes from that era came with an eclectic and international mix of parts. Swiss, French and Japanese parts would be happily mounted together on the same bike in the factory, with function, availability and price point being the main considerations. The Belgians (Flandria) were also the first Europeans to pick up on Shimano's potential, closely followed by the Dutch (Koga-Miyata).
Gazelle spec'ed one of their Champion Mondial versions in the seventies with parts from Reynolds (frame tubes), MKS (pedals), Gian Robert (hubs), Arius (saddle), SunTour (derailleurs), Weinmann (brakes), Sakae (seatpost), T.T.T (bars), Sugino (crankset) and Super Champion (rims).
I wouldn't worry too much about what's "right".
