Haven't gotten the box so I haven't read the notes. If he doesn't mention Cooper, who I'm sure is credited for his performance in the discographical information, perhaps he's not familiar with his work. In order to write the booklet, he should have been. Maybe he's just young.
Much to do about nothing: The notes say "Altschul" twice instead of "Cooper". There's no extensive analysis of the percussion work on that session. (A quick look in his book confirms that he knows it's Cooper on that session.)
And, fyi, Heffley is three years younger than Braxton. I'll let you determine the proper age-to-typos ratio for music scholars.