Check the first publication date of the Prokofiev work you arranged. You are from USA. Romeo and Juliet was written in 1935. Assuming it was first published in 1935, it will not be in the public domain until 1/1/2031 at the earliest. Prokofiev died 1953.
United States:1) Any work first published before 1928 is in the public domain. Example: Prokofiev's Piano Concerto No.1 is public domain in the US, since it was published in 1912.
2) Any work first published from 1928 to 1977 is subject to a 95-year term of copyright. (As long as a renewal 28 years after first publication was filed on time!) - This is case for Prokofiev and other Russians
3) Any work first published 1978 and later is subject to a term of life of the last surviving author plus 70 years.
https://imslp.org/wiki/IMSLP:Copyright_Made_Simple2nd scource for confirmation: For USA: 95 years from first publication for works first published 1928–1977
https://en.wikipedia.org/wiki/List_of_countries%27_copyright_lengthsAs mentioned in prior post, if your Prokofiev work that you arranged is NOT in the public domain based on when it was first published and the above mentioned rules: The unauthorized adaptation of a work may constitute copyright infringement.
My suggestion - Keep your Prokofiev arrangement out of the public in USA until 1/1/2031, assuming it was first published in 1935. You need to verify the first publication date.
Then when it is in the public domain - unfortunately 8 years from now or more:https://www.copyright.gov/help/faq/faq-general.htmlQ: Do you have to register with the U.S Copyright Office to be protected?
A: No. In general, registration is voluntary.
Copyright exists from the moment the work is created. You will have to register, however, if you wish to bring a lawsuit for infringement of a U.S. work. See Circular 1, Copyright Basics, section “Copyright Registration.”
If you need to register your work, follow Circular 14 instructions:
https://www.copyright.gov/circs/circ14.pdfCopyright Office website at
www.copyright.govDisclosure: I am not an attorney nor have I ever obtained a copyright for music. The following was obtained from a quick google search and quick reading of Circular 14. See what others have to say here.
Good luck!