In Europe and Russia, all Medtner's works will be in copyright until 31 December 2021. There was a period between 2001 and 2007 when Medtner's works were out of copyright in Russia, and Opp 33-37 in Europe too by virtue of being first published by the Soviet musical press, but this changed with a new Russian copyright law that came into force in 2008.
In the USA, the current 70-year rule does not apply to works created before 1978. Works published before 1923 are in the public domain. This applies to all Medtner's works up to Op 38 plus Op 40. Works published from 1923 have an initial copyright period of 28 years which is extended to 95 years if copyright was renewed during the 28th year. IMSLP regards all works apart from Op 58 and the piano quintet as definitely or very likely to be out of copyright in the USA.
Medtner's works are in the public domain in Canada, Japan, China, South Korea, Australia, New Zealand and many other countries.
In the UK, copyright in a published edition expires 25 years from the end of the year in which the edition was first published. Typographical copyright does not exist in the USA.
In the UK, a new copyright law came into effect on 1 November 2013 that will eventually be harmonised across Europe. For recordings that were in copyright on 1 November 2013, protection now lasts 70 years from the end of the year in which a recording is published or otherwise made available to the public (e.g. by broadcasting); or for unpublished recordings, 70 years from the end of the year in which it was made. Recordings out of copyright under the previous 50-year rule, i.e., recordings published before 1 November 1963, remain out of copyright. For recordings made before 1 June 1957, whether published or not, copyright in the UK lasts 50 years from the end of the year in which the recording was made.
In Russia, recordings are in copyright for 50 years after the end of the year in which the recording was published or broadcast. This differs from the 70-year rule applied to scores.
The situation is more complicated in the USA. Recordings are generally protected either for life + 70 years or 95 years after creation, but some recordings made before 1972 will be protected by state law until 2067 regardless of their date of origin. Laws in other countries vary widely.
There has been some debate as to whether digital remastering of old recordings can create new copyright. The consensus of legal opinion is that it cannot.