Getting back to the subject of schedules for a moment, while doing a Google search for links on NFL by-laws, I stumbled across the following book:
Pro Football Schedules — A Complete Historical Guide from 1933 to the Present by Ivan Urena. It was apparently just recently published (its copyright date is 2014). The Google Books link to it—which contains previews of some of its pages—can be found
here. Just scroll and you can see the pages from the book that are free to see. It looks to be a very detailed work.
One lucky break is that the playoff matching system in use in the NFL from 1970-74 (which used a rotation of home field advantage amongst division winners rather than seeding) is shown in one of the preview pages. I always wondered exactly how that worked.
(Side note: I did find a PDF copy of the 2006 NFL By-Laws available online.)