If an NPC's strife becomes relevant during a scene (because they get some strife through skill checks or the PCs actions), do you start counting from zero? Or would it be fair (towards the PCs) if NPCs in such cases could have at least sometimes already a bit of strife. Logically they would have some, since they probably did some checks in the last time (and you can't drop to zero per sleeping), but on the other hand it would require hand-waving to determine how much strife they already got. If you do so, what could be a reasonable amount? I'm thinking along the lines of 'usually 1 or 2, but occasionally up to half their composure'. Maybe, if the NPCs situation warrants it, it could be even more, but in that case you probably already kept track of its strife before.
Of course, this would only be relevant, if the NPCs strife could possibly be important/interesting for the current scene.