Originally posted by monochrome In the West, northern hemisphere, ‘summer 2018’ begins June 22nd
Actually, as you know, at least three definitions of "summer" are used in the US:
(1) the one you used
(2) weather people say "summer" is June - Aug, the three warmest months
(3) culturally, "summer" begins Memorial Day weekend {past} and ends Labor Day weekend {yet to come} - this definition is (2) with a week or so added at each end
I'm guessing we can't expect a Japanese company to use anything based on U.S. practices, but I've never seen them say anything with that kind of precision, so we're probably "over-thinking" this again.