Many historians have now cross referenced known facts about Indian culture with the data in these old books and found many of the old books greatly wanting. Even works by scholars of the highest caliber like John Swanton or H. E. Bolton and even Newcomb contain biased steriotypes and have a good deal of information that has proven to be inaccurate using new information from new research. Newcomb starts the book with false, rather racist, negative stereotypes of two major subgroups of Indians. The barbaric gardeners Newcomb is refering to include the very civilized Caddo, the complex Jumano, and the Witchita. The Caddo, Jumano, and Witchita are hardly barbarians by any standard.
Experts know what parts of older works to accept and what parts to be skeptical of.
A non expert cannot do this and has a real problem using much the information in many of the older works. When kids try to use this material it results in a huge waste of time and some really crazy ideas. The other is to put an end to many of the old racist stereotypes that have caused so much harm. Because this site is for kids. AND, because I am a big kid myself.