For Japanese books, the following seems to be applicable

http://www.cric.or.jp/cric_e/clj/
http://www.cric.or.jp/cric_e/clj/cl2_2.html#cl2_2+S4
Article 51.
(1) The duration of copyright shall begin with the creation of the work.
(2) Copyright shall continue to subsist until the end of a period of fifty years following the death of the author (or following the death of the last surviving co-author in the case of a joint work; the same shall apply in paragraph (1) of next Article), unless otherwise provided in this Section.

http://en.wikipedia.org/wiki/Copyright_law_of_Japan
Note that wikipedia has the following note, but uncited:
Japan is considering extending the duration of protection to seventy years to be more in line with the United States and other nations.

But this probably cannot be applied retrospectively.

Why is this important for the game of go?
Go has had a very very long history and there are many wonderful Japanese authors of the past who have died more than fifty years ago. So it would seem their works would now be copyright-free. This means that, not only do we not not need to worry about ancient problem collections, but also that of composers of tsumego problems who have died more than fifty years ago. However, this only applies to the tsumego problems presented as is when it was first published. It doesn't apply to more recent revisions or corrections of the problems by other authors who are still within the copyright protection period. And remember that some modern versions of ancient problems have had correction by more modern authors to mistakes that made the problems unsolvable or answer variations which overturned the thoughts of the ancient.

In the case of Kada Katsuji 加田克司, according to SL, he died in 1996 so his work still has plenty of time to be under the control of his heirs.

Why would I be so interested in the above?
Because there are at least two significant works of Japanese tsumego whose sole author have died prior to 1962 (thus more than fifty years ago). And I'm talking about works which were published after Honinbo Shusai's Shikatsu Myoki
So theoretically these works are now copyright free and anyone can legally translate the whole collection of these tsumego into English for publication and distribution. Of course if you do attempt to make use of such copyright-free collections, you should make sure you use the original work and not a modern reprint of the original work which may include revisions and additional writings by more modern authors as such would most likely still be within copyright protection period. Don't ask who and do your own research if you want to find those collections yourself.

I am not a lawyer though so don't take my statements above as the absolute final say.