I imagine Anduriel knows, thanks to the powers of being a fallen angel.
Id go with that. They still follow Rules, just Rules that we wee mortals have difficulty understanding. Or TWG informed the knights somewhere/somehow along the line (seems like the sort of thing the rules would allow the Knights to know).
Yeah. You know what's funny. When Murphy made her error against Nicodemus, he in turn error'd against the Sword. He took the Sword, and broke it on the ground because he didn't have Faith the Sword could work without the blade. The correct way is to unmake the Sword by killing an innocent with it.
That's how you destroy Amoracchius (aka the Sword of Love), which as cold-hearted murder of an innocent is arguably a supremely Loveless Act. The Sword of Faith is Destroyed by Faithlessness, or an act of treachery (per SmF). Im guessing the Sword of Hope would be destroyed by an Act of Despair where somebody would need to commit suicide on it.
But the other aspect is that, per GP, a Swords destruction is a two-stage thing. First it needs to be made Vulnerable through mis-use, rendering it a mundane sword the way Harry did with Lea that time. Then, once a wielder has exposed it the final destruction can be done, which was where Mavra was going to murder an innocent with it. It's possible that Nic was hoping Murphy's strike would be enough internal/emotional betrayal to do the deed, but I think it more likely that he just went for the lesser Win. Even if the Sword's magic/spirit wasnt permanently destroyed it
should have taken months or years to reforge the Sword into something that would actually threaten him; ensuring that one of the defunct swords stays defunct is a Win for him, especially now when all the Big powers are realizing the clock is almost out, so a few years more is all that really matters.