Our church has a Yamaha C7.  I believe it is around 35 years old.
It has the Japanese Yamaha logo rather than the English one.  Not
knowing the full history of the piano (it was given to us as a gift,
used), I wonder if the logo indicates it was originally destined for
the Japanese market.

In any case, our building is quite dry -- heat/AC only, no humidity
control -- and it does have a noticeable effect on the piano.  While
the pins are still relatively tight and the wood does not appear to
have sustained any damage due to moisture loss, the piano is quite a
bit more sensitive than our Kawai upright practice piano in the same
small building.

In winter, the Yamaha tends to go out of tune rather quickly (on the
order of a couple of weeks), primarily in the area of the treble break.
We recently had a DamppChaser installed in an attempt to moderate the
effect of the dry air.  It seems to help, as long as it is kept filled.
It only takes a few days of dry air to take it out of tune again.

In regard to the Japanese climate, it might help to remember some parts
of the country have a rainy (monsoon like) season in addition to the
usual four.  Being a long thin island in the Pacific does tend to
contribute to high humidity. :)  Also, the typical Japanese home of
before mid-last century did not have central heating and so would have
less problems with dry air.

Mike Blackwell