What is the purpose of the doors in series requirement and how should it be applied in configurations other than those shown in the Figures in the Standards?

My understanding is that it was written to keep wheelchair users from having to fight two doors at once.  It was an expansion of the 1961 A117.1-1961 requirement that said at least one leaf of a pair of double doors had to be accessible.  I think I heard that explanation from discussions with some of the old-timers/access pioneers involved with writing ANSI A117.1-1980, UFAS, and the 1984 CBC where the requirement first appeared.  The 1984 CBC has a note in the figure attached.

There was never really consensus about what was required for doors in configurations other than what is shown in the Figures from the Standards (such as in vestibules where the doors are diagonally opposite) until the Access Board created the second figure attached to clarify the intent.

To summarize my opinion, you need compliant door maneuvering clearance at each door, AND space to avoid fighting two doors at once.