Vagabond -
From Dictionary.com:
the flying of an airplane on a combat mission.
Why the ambiguity? Probably because they don't want to give an exact number.
They know EXACTLY how many flights there were on any day - if you care to look deep enough.
Yes - pilots know how many sorties they have flown through a variety of means. All the same types of paperwork that any pilot / company keeps.
USMCFLYR