Providence,
The results take place immediately, not at the end of the round, which is why if you're stunned after you've expended your activity for the round, this round doesn't count. . .i.e.:
In round 1 Godfrey hits Bruce with a Club, and stuns him for 3 rounds. . .if Bruce already attacked and expended action this round, he will be stunned for rounds 2, 3 and 4 (3 rounds). But if Bruce has not yet acted, he is immediately stunned, and will be stunned for round 1, 2 and 3.
So the upkeep as you transition from the end of a round to the start of the next is the point where you tick off rounds of multi round effects like stun, spells, etc. . .but if you're stunned, killed or injured before you get to go, you're stunned killed or injured immediately, before you get to go, not at the end of the round.
MarkC,
Example 1
If Godfrey and Jeeves are attacking Bruce with Clubs at 100% action. Initiative order works out to Godfrey going first, Jeeves second, and Bruce third. So both attacks are in the same phase, at the same amount of activity, separated only by initiative, so they are as close to "happening at the same time" as things get.
Round 1
Godfrey attacks and hits Bruce, crit result includes "2 rounds Stun and Unable to parry" Bruce is immediately SNP, and because he has not yet acted this round, the SNP will be this round and next.
Jeeves attack on Bruce, Bruce is stunned and unable to parry. . .so the bonus for stun applies, and the parry DB is already negated by the NP part of the SNP.
Lord Miller,
You do not know when in the round the shield was shattered as the % action just tells you who goes first not which damage is applied first.
Also the PC who downed his foe does not know he is dead. He does not know the NPC's hits, recovery rate, regeneration, etc. He just knows he is going down for some reason. Maybe it is a feint or some other move.
MD
I agree that Jeeves may not know Bruce is stunned no parry, he could be faking, but regardless if he knows or not, Bruce is still stunned, and may not parry.
Example 2
Lois, Kal and Clark are fighting. Lois and Kal have initiative.
Round 1
Lois hits Clark, Crit result is a knockdown prone.
Kal's iniative comes up, he gets vs prone attack bonus on Clark. . .
Clark's initiative comes up (if Kal doesn't kill him) he can take the from prone penalties, or abort attack to stand up again.
Again MarkC, I agree that Kal doesn't know if Lois knocked Clark down, or if Clark is faking and dropped. . .but he still gets the bonus vs prone target to his attack.