Please note that Canada has amended its copyright laws. Since the IMSLP servers are based in Canada, this is relevant to uploaders and users.
All works by people who died in 1971 or earlier are in the public domain and remain in the public domain.
All works by people who died in 1972 or later now receive 20 years of extra copyright protection. As such, these people's works do not generally enter the public domain in Canada this year.
However,
Since Canada does apply the Rule of the Shorter Term for authors who are not nationals/citizens of the United States or Mexico, works originating from countries where the term of copyright is shorter (e.g., New Zealand, China) may still be added if they are in the public domain in their home country.
Works published in 1927 or earlier are eligible to be added to the US server in 2023.
Additionally, in the future, a linked server may be set up in a country that has a 50 years p.m.a. copyright term to host files that are in the public domain there.