those old books are still good though. There's only new syntax for latest ruby versions.
Anyway, there have been updated versions of the books and content online if people are interested.
Most changes have been in libraries and interpreter / VM implementation.
Updating your knowledge from Ruby 1.8 (mid 2000s) to 3.x (current) takes little effort.
But yes, sparse API documents were always a problem because a big chunk of the community was Japanese.