I am not an attorney and any comments I post are not intended, nor should they be construed, as legal advice. If you need legal advice, please consult a legal expert who is familiar with the area of legal expertise you need.
A friend asked me about copyright as it relates to Sherlock Holmes. For the most part, a large portion of the written works are in the public domain. I will use the date December 31, 2018 and reference U. S. Copyright for a lot of this post as January 1, 2019 saw anything published in 1923 fall in the public domain for U. S. Copyright purposes.
Here are several articles, mostly from pre-2018:
https://www.telegraph.co.uk/film/mr-holmes/sherlock-copyright/ (2015) – had trouble getting anything on this link for some reason,
With American copyright law only extending 95 years after publication, 46 of the 56 Sherlock Holmes stories and all 4 novels were in the public domain. The final ten stories, collected in The Case-Book of Sherlock Holmes, were all published from 1923 to 1927 and will enter the public domain one by one up until 2023.
Wikipedia on the last collection: https://en.wikipedia.org/wiki/The_Case-Book_of_Sherlock_Holmes which indicates 9 of the 12 are still in the public domain.
The copyrights for Doyle’s Sherlock Holmes stories expired in 1980 in Canada and in 2000 in the United Kingdom. In the United States, the only Sherlock Holmes works by Doyle still protected by copyrights are nine of the twelve short stories from The Case Book. The first three stories (“The Adventure of the Mazarin Stone”, 1921; “The Problem of Thor Bridge”, 1922; and “The Adventure of the Creeping Man, 1923”) are already in the public domain since they were published before 1924. The other stories will enter the public domain on 1 January of the year after the 95th anniversary of each story’s publication: 1 January 2020 for “The Adventure of the Sussex Vampire”, “The Adventure of the Three Garridebs” and “The Adventure of the Illustrious Client”; 1 January 2022 for “The Adventure of the Three Gables”, “The Adventure of the Blanched Soldier”, “The Adventure of the Lion’s Mane” and “The Adventure of the Retired Colourman”; 1 January 2023 for “The Adventure of the Veiled Lodger” and “The Adventure of Shoscombe Old Place”.
https://www.ihearofsherlock.com/2015/07/the-scandalous-sherlock-holmes.html (2015) – a great explanation of the convoluted debate as to who owns the remaining 9 or 10 works that are still under copyright in the U. S.,
https://www.robertreeveslaw.com/blog/sherlock-holmes-belongs-to-everyone/ (appears to be a law firm; 2015), this was written before 1923 published works became public domain
Out of a total of 56 short stories and four novels to feature Sherlock Holmes, a final 10 short stories that Doyle published between 1923 and 1927 are still in copyright.
https://www.arthurconandoyle.com/copyrights.html (The Official Site of the Sir Arthur Conan Doyle Literary Estate, one of two estates that may control copyright on Sherlock Holmes and you may want to make sure the other estate doesn’t claim copyright before proceeding). It lists two (2) works that fall out of copyright as of 2019. It lists more than ten (10) works which is at odds with other links that indicate as of December 31, 2018, only 10 of the 56 written stories were still protected by copyright. In this case, I am referring only to the written works as movies usually have different copyright dates for things that are unique to the movies that weren’t in the short stories or four novels written by Sir Doyle.
This may be the other major claimant to holding copyright on Sherlock Holmes: https://conandoyleestate.com/index.php although it may not be the only other claimant.
As long as you go with the works that are in the public domain and don’t reference any creative aspects that appeared in the works still under copyright or any creative elements of the 200 movies that weren’t in the published works, you should be fine. However, that’s not to say you won’t be sued by one or more of the potential claimants who believe they own the copyright.