Sorry, yeah, some of the details were a bit muddy. That part meant only the group leader is considered for spawning encounters at all. So if the leader wasn't On Patrol but they had five members who were, they wouldn't spawn any patrol encounters because the leader is not currently on patrol. So we don't run into situations where some group member forgot to remove their tabard (or put it on for whatever reason) and now suddenly the group is getting a bunch of encounters when they weren't gathered for that purpose.
Q) each and every patroller receive merit for each mob slain? each and every patroller receive merit for each patroller-spawned mob slain? (if it generates a mob for each person)So if a group full of On Patrollers are roaming around along with some non-patrollers, and a stack of seven mobs spawn, will...:
A) As long as they're flagged as On Patrol and they've landed some kind of hit/maneuver/etc. (same as credit for experience gains) on a patrol-spawned mob that is defeated, they'll receive merit. In the case of a mixed group of On Patrol and non, every mob spawned will be considered patrol-spawned and be eligible for merit so long as the group leader is On Patrol.
Q) only the mob they themselves spawned among the group grant them credit? only the leader get credit because they spawned them all?
A) Patrollers can get credit for any patrol-spawned mob, regardless of who spawned it. So if you wandered into a mob spawned by someone else (maybe they had to run or they got killed) and you land a hit of some kind on it and it's defeated, you'll get merit for it even though you weren't around when it spawned.
Q) do you need the killing blow to get merit?
A) Nope, as long as you're On Patrol, the mob is a patrol-spawned mob (regardless of who spawned it), and you've landed some kind of hit/maneuver/etc. on the mob, you'll get merit when it's defeated.
Q) do you need damage credit to get merit?
A) Not strictly damage - things like dirty tricks or spell effects or anything else that counts for Experience gains credit also count for merit credit. (incidentally, if there are any effects that don't count but probably should, please do report them with the BUG command in-game or if you're unsure, you can suggest it here in this thread.)
Q) does it not matter just as long as it dies, period, you'll get merit?
A) If you didn't manage to land anything on it, you won't get merit.
TL;DR: If you're On Patrol, and the mob was spawned by someone who was On Patrol, and you landed some kind of hit/debuff/effect on it, then you should get merit for it when it's defeated (including if it flees and despawns, but not if it despawns from being neglected).