Professional writers will look for many sources to strengthen their writing because that is what a writer should do. If it is true that the author of the book did not learn the complete truth about Bitcoin then the book is not worth reading because it will create a misleading understanding for those who read it. That's why not all books are worth reading, and vice versa regarding videos made by people who don't have a clear source of truth.
The conclusion may be that the author is not very professional because he risked his credibility after publishing the book and now almost many people will never want to follow his writing after the facts about the book are quite misleading. Almost everyone knows the fact about four years in Bitcoin and maybe we need to provide education about this to the author of the book.
What you say is very correct, of course we don't need to read books whose authors don't have clear reference sources because this will make it difficult for us to invest in Bitcoin and if we choose to read a book we have to first find out the background of the author, whether it is true. Whether an author has clear references or not, some people who make videos sometimes just take advantage for themselves and don't care whether what they say is in accordance with existing reality or not.
When someone finds out that the book they are reading contains wrong understanding, of course they will never read the book again and will look for a book that has an explanation and a clear reference source.