There are currently only a few such courses on Chessable. Most courses are written by the authors themselves and this does not apply to them.

A verified endorsement of a course means that a titled player has reviewed and approved the variations that this course contains. Titled players are often extremely busy pursuing their careers, and hence, Chessable offers the opportunity for their students to bring their courses to Chessable while allowing the titled players the credit they deserve for helping compile such masterpieces.

Most, if not all lines in an endorsed course have been hand-picked by the titled player. However, usually support, and commentary are provided by the course owner who may not be as highly ranked but can provide some guidance. It is then up to the community to bring the course up to a level they desire by collaborating together on the variations included.

By working on such a model, Master-quality courses can be available on Chessable at a lower price than if the course was fully maintained by the Master themselves.

There is a blog post written with more details here.