Should we obtain formal name use permission for endorsements

Hello, we have not sent out requests for endorsements but we are receiving interest from people who know some of the individuals involved in the project, and they have agreed to give an endorsement after reviewing the book. These include a Grammy award winner, someone who has reviewed the Van Halen book, and others. Is it wise to have them sign some type of release? A couple of them have indicated they are willing to do so, but is it a necessity? Thank you in advance for sharing your experience.