The issue is that if "No parry" is a separate status that's not stun, does that mean that only "No Parry" that exist stand alone will affect stun immunes like undead, and are non curable by unstun, and stack with other stun effects. . .
Or if it's always independent, so if you are Stunned + No Parry then will that just "No Parry" an immune like an undead, and that an unstun will just shift you from SNP to "No parry".
And if indeed "No parry" and "Must parry" are not stun, then does it stack in duration the way only stun results do RAW. . .so that 5 separate "No Parry" or "Must Parry" results last for 5 rounds, the way 5 separate "Stun" results last 5 rounds.
Not denying the benefits of a non stun type of staggering or unbalancing type crit result, just pointing out that the devil lies in the details, as usual.