Harry, impossible to kill?

[allies426]

No: HPFGUIDX 177593

Deathly Hallows, 708, US:

Harry:  "He took my blood."
DD:  "He took your blood and rebuilt his living body with it!  Your 
blood in his veins, Harry, Lily's protection inside both of you!  He 
tethered you to live while he lives!" <snip> "His body keeps her 
sacrifice alive, and while that enchantment survives, so do you and 
so does Voldemort's one last hope for himself."

This means that it is *impossible* for Harry to be killed by 
Voldemort after he is reborn.  So except for a few happy 
coincidences, the scene at King's Cross could have happened any 
number of other times:

1.  In the graveyard in GoF - Harry and Voldemort dueled.  Even 
without the twin cores, Harry could not have died.  

2.  The MoM in OoTP - Voldemort fires an AK at Harry, and he is 
saved by a piece of the statue.

3.  The chase seen in the beginning of DH - Harry's wand 
miraculously "regurgitates" some of Voldemort's magic at him, but 
even if it hadn't done that, it wouldn't have mattered.

Why, then, did the rebounding curse rip Voldemort out of his body 
when he attacked Harry in Godric's Hollow, but merely knock him out 
for a few minutes in the forest?  Was it the addition of the Nagini 
horcrux (the Harry-horcrux having been destroyed by his curse)?  Or 
did the curse *not* rebound on him, and if not, why not?  

In fact, if the blood protection is still in effect, does that mean 
there was no way EVER for Voldemort to kill Harry?  That Lily's 
sacrifice endowed Harry **forever** with protection from Voldemort's 
AK?  Then why didn't Voldemort realize this, and let someone else 
finish Harry off?  He admits that he didn't realize the power of 
what Lily did until it was too late.  Why does he think it would 
only work that one time?  

Before the Horcruxes were destroyed, Voldemort could have fired 
curse after curse at Harry and still not killed him.  

Allie
(who gets more confused the more she thinks about these things, and 
is now so confused that she hopes some kind soul will help further 
muddy the waters... um, clarify things)