EDIT: read the ownership dispute & history[1] at wikipedia - it certainly reads like various inheritors (heirs?) have gone to some lengths to extend the copyright of the original material by making periodic changes. I am not a lawyer, consequently I don't understand how such changes can affect status of original work (as in - how they can apply retrospectively to the original work - and not just affect copyright of those changes).
Heirs and descendants are not synonymous.
EDIT: read the ownership dispute & history[1] at wikipedia - it certainly reads like various inheritors (heirs?) have gone to some lengths to extend the copyright of the original material by making periodic changes. I am not a lawyer, consequently I don't understand how such changes can affect status of original work (as in - how they can apply retrospectively to the original work - and not just affect copyright of those changes).
[1] https://en.wikipedia.org/wiki/The_Diary_of_a_Young_Girl#Copy...