this is the brilliance of cryptography, in essence the “uniqueness” doesn’t need to be ensured.

the npub that can be trusted has all posts signed by a valid signature from its nsec.

so long as the post is signed, the npub is verified to “belong” to the nsec.

even if someone had custom derived 1 million npubs from their nsec, each new npub requires a signature to be trustworthy.

all posts on nostr are signed or they are not valid! so there’s no database needed, only a protocol which ensures that strong cryptography is being used.

now, you can’t verify that new npubs are unique human beings in real life, but that is why in the information age we must verify the content provided and not concern ourselves only for sources.