Books without a copyright can be difficult to date accurately, as there is no official date to refer to. Generally, if a book was published before 1923, it is in the public domain, meaning it is free to use and distribute without permission from the author or publisher. This is because the copyright law at the time only protected works for 28 years, and any works published before 1923 have long since expired.
If the book was an unpublished work, and the author died over 70 years ago, it is also in the public domain. This is because copyright law protects works for the life of the author plus 70 years. If the author died over 70 years ago, the copyright has expired and the work is in the public domain.
Finally, if the book was written by an anonymous author over 120 years ago, it is also in the public domain. This is because copyright law protects anonymous works for 120 years from the date of publication. If the book was published over 120 years ago, the copyright has expired and the work is in the public domain.
In conclusion, determining the age of a book without a copyright can be difficult. Generally, if the book was published before 1923, or was an unpublished work and the author died over 70 years ago, or was written by an anonymous author over 120 years ago, it is in the public domain.