Did JRRT encourage new ME stories?

[Sauron the White]

This is from Wikipedia in the article on copyright law.

Copyright subsists for a variety of lengths in different jurisdictions, with different categories of works and the length it subsists for also depends on whether a work is published or unpublished. In most of the world the default length of copyright for many works is generally the life of the author plus either 50 or 70 years.

Can anyone identify the reasons why with Tolkien it would be 75 years as davem provided in his latest post? Also does anyone know what determines if it is 50 years or 70 years? Does this mean that - in some parts of the world - we could be looking at the issue 50 years after the 1973 death date? That would mean 2023 which is 16 years away.

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more info... The revised British law recognizes 70 years after an authors death. Before the mid 1980's it was only 50 years. Some other countries have shorter periods.