Complexions & Colour
Thinking back to conversations with my father, I believe I recall him saying that the Kodak labs would process their Kodachrome and Ektachrome to slightly different targets, depending on where they were located. As a result, it may have been the case that film processed by Kodak Japan would be more flattering to Japanese complexions then film processed in, e.g, Palo Alto, California.
I believe they would also vary somewhat at different times of the year - summer photography and Christmas photography have different tendencies.
You have to remember, of course, that this was at a time (the late 1960s to the early 1980s) when slide film and movie film volumes were huge, because many amateurs with very basic photographic needs were using those materials.
The other thing I remember when I see comparisons of this type between Kodak and Fuji is an observation of my father's - one of Kodak's largest markets for film and processing was in Japan, and they were very interested in maintaining that.