20. The duration of Public Lending Right in respect of any book and the period during which there may be dealings therein shall be from the date of the book's first publication (or, if later, the beginning of the sampling year in which application is made for it to be registered) until fifty years have elapsed since the end of the sampling year in which the author died or, if the book is registered as the work of more than one author, as regards dealings in the share of the Right attributable to that author, the end of the year in which that author died.