There is a lot of confusion around where it was made VS JDM's...
A g-shock bought in 1992 and was manufactured in 1991 must have been made in Japan because G shocks were all made in japan back then.
I've heard about 5600c batteries lasting 20 years but that's nothing to do with the country of origin. Later, Casio started making G shocks in China, Malaysia, Thailand and...?
There are models that are still made in Japan, mostly the expensive lines like the MRG.
There are models that are designed to be sold only in Japan but sometimes those are made in a different country.
I have a DW-6900 "made in Japan" and another one "made in china". I can't tell the difference in quality.
That's my take from what I know and understand, so take it with a small grain of salt...