By the way, Igo Daijiten is copyright free.
To quote from the editorial note cited at Igo Daijiten / Background at Sensei's Library (emphasis mine):
This book was not created overnight. The late Suzuki Tamejiro conceived this project 50 years ago, and, whenever the occasion arose, collected patterns diligently. After further research on these patterns he published the book for the first time in 1933.
However, because of the war later, it was all reduced to complete destruction and so, some ten years after the war, having obtained the support of Ogawa Kikumatsu, then Chairman of Seibundo Shinkosha, Suzuki decided to proceed with publication, after more than 32 years, of a revised edition to which he had added fresh text.
On 3 November 1960, when he had completed all three volumes of this new edition, Master Suzuki received the Medal with Purple Ribbon because of his meritorious service in which he had devoted himself to the development of the go world over many years. But on the 19th of the same month, he unexpectedly collapsed while chatting with the group of our editorial team attending the celberation of his award. He died suddenly the following day, the 20th.
Referring now to Copyright law of Japan - Wikipedia
The 1899 law protected copyrighted works for 30 years after the author’s death.
The copyright was initially set to expire in 1990.
Law changes promulgated in 1970 extended the duration to 50 years
The copyright expiration date advanced to 2010.
However, in 2004 Japan further extended the copyright term to 70 years for cinematographic works.
This is a book, not a piece of film.
At the end of 2018 … the 70 year term was applied to all works. This new term was not applied retroactively; works that had entered the public domain between 1999 and 29 December 2018 (inclusive) due to expiration remained in the public domain.
Therefore we can conclude that Igo Daijiten left copyright in 2010, and has been in the public domain ever since.
Would you be happy to scan the book and upload it somewhere, Atorrante, if no-one else has done so already?
(Also worth noting that Modern Joseki and Fuseki was only published eight years later but is receiving, at this point, at least 81 years more copyright.)