Well, here's the whole order:
http://www.regulations.gov/#!documen...2008-0367-0002

Based upon the discussion, it would seem that itinerary is meant to include an entire reservation/PNR.
The answer to the question posed in the OP, is that A to B and B to A is one itinerary for the purposes of this rule (assuming one reservation record) because the order explicitly discusses to/from.