Their sales in gross dollars have increased significantly. All of the authors whom I have represented over a period of years have increased their earnings. The average is about four times as much as they earned in 1980. I cannot tell about all the authors. Though there is a pattern of increased income, they are all quite different.
Some authors are far more prolific than others.
Needless to say, people who produce more books and sell more books are increasing their earnings at a significant rate. Generally speaking, most authors should be doing better. There are far more books being published now. Ten years ago, there were approximately half the number of books published in the children's book field than there are now. We now have approximately 5,000 new books coming out every year.