Wasting assets: copyright
The copyright in any work runs for a specified period. Currently, it runs for 70 years after the end of the calendar year in which
- the author, etc, dies
- the work is first published or produced.
Thus, if copyright is acquired by a person 20 years or more after the end of the year in which the author died, it is then a wasting asset.
Before extension to 70 years copyright ran for 50 years and was a wasting asset from the end of the year in which the author died or the work was first published or produced.
CG68250 tells you more about copyright.