You might be looking for an undercover expose. Or a former employees tell all. Trouble with those is they are often misleading and slanted resulting in skewed or meaningless conclusions....and they don't result in a second book...
As a real journalist Holley knew that and what he set out to do was learn as much about the inner workings of this organization as he could and utilize that information to help him understand what they do and why they do it and give his readers the benefit of that insight. Had Ron Borges spent that amount of time imbedded with the team his read on them and his agenda driven mantra likely would not have changed one iota - he'd just have had a lot of anti Belichick secrets to tell along the way to underscore his existing agenda. Michael went in without an axe to grind and just wanted to see for himself why they did things the way they did and document the outcome (which by the time his book came out was increasingly clear...they were building a dynasty).
Had the ambitious yet insecure Felger done the book it would have been unreadable (he's really a sports mediot, not a writer and certainly not a journalist) and we'd have known all the little secrets he uncovered long before the book hit the stands because in order to advance his radio career and prove to his peers he was an insider he'd have leaked them. Felger used to car pool to the stadium with a certain QB until he started ripping other athletes and revealing things he was told off the record to advance his radio career. He also used to get tutored on the the ins and outs of both the on and off the field systems by Belichick and Jonathan Kraft until he started attacking their approach for the same reason. Nowadays listening to his infrequent interviews with any team insider is almost painful as he goes into attack mode or attempts to set them up and they either spar with him or give him canned answers...and the result is we the listeners learn nothing beyond Felger has redundant agendas.
I'm sure Michael saw and learned things about the Bruschi's that weren't included in that book because he didn't need to include them to write a good story. Tedy obviously knew he could trust Holley to write a good story about his life without exploiting his family based on the way he handled the book about his team. Ditto Halberstam and Education of a Coach. His book was a journalists homage to the father son coaching phenomenon, not a titilating tell all BB biography which neither Bill nor any associate worth interviewing would ever have cooperated with. Real journalists don't set their subjects up to be personally embarassed or professionally humiliated for cooperating. You don't gain trust that way. You treat them fairly, and part of that is having some discretion in exactly what you use and how you use it relative to what you are allowed to witness or know. Some of it remains in background simply helping you form and frame conclusions you share with your readers with a greater level of confidence. One approach may help you sell one book. The other allows you to author many bestsellers.