Ignore it all you like, it's what the rules say.
No they don't say that. It is what you cliam they say and it is preposterous.
If they really said what you claim you would be able to provide the exact wording supporting that claim and you can't.
"you typically show no signs of injury. When you drop below half your hit point maximum , you show signs of wear"
Again you avoid posting what you are actually claiming. Being injured and showing signs of injury are not the same thing, no matter how many times you post this over and over again.
Also the wording is actually contradictory to your claim. You claim is only the hit that causes 0 hps does actual damage, yet any hit point that takes you to 50% would cause you to show cuts and bruises. Are cuts and bruises not "actual damage"?
How do explain cuts and bruises on someone who has taken no damage?
How can something be "bloodied" when it has taken no actual damage?
While I am at it a few more questions:
1. why do casters need to make Concentration saves repeatedly when they are taking no damage?
2. How does a spell like Magic Missile actually miss you when the spell says it strikes a target?
I Now what sort of exception would necessitate signs before you hit 50%? I know! I stinger with poison!
It is not an exception and I posted an example of a monster that goes into "blood frenzy" against enemies that do not have all their hit points. So a PC gets hit by a dagger, that does no actual damage, and a half hour later he jumps into water and the Shark he is facing goes into blood frenzy .... even though he has taken no actual damage.
So then stop quoting something out of context! The wording you keep quoting is there as a framework to describe the abstraction of hit points, it is not there to be an arbiter of when someone has or has not taken "real damage".
You keep using that wording out of context!
Just face it you are wrong, and admit you were mistaken.