They are saying that when an author is looking to sell the rights to their work, the price of that work is discounted based on the expected lifetime of the auth

They are saying that when an author is looking to sell the rights to their work, the price of that work is discounted based on the expected lifetime of the author. So in a parallel universe where the same work is written by a 20 year old and an 80 year old, the 20-year-old artist can sell the perpetual rights for more than the 80-year-old because the new rights holder will get 60 years of protection in the former case and only 10 years in the latter case. I don't think I agree with the GP on the conclusion, but this part anyway seems logically sound to me.