For the Vampire Killer to be made, a WILLING vampire soul with a connection strong enough to enter a blood pact with the other party is required "You need a tainted soul, one that trusts you and one that you can trust". That's what makes the chances of creating the Vampire Killer at that precise moment so extremely unique. Sara is already tainted, and she's willing to give up her own tainted life to save others. The old Christian tale of the innocent soul sacrificing willingly to save humanity, kinda. Had Leon waited for the vampirism to take over, the blood covenant couldn't be made anymore. Afterall, even tho Rinaldo slain his own daughter turned vampire, that didn't make the Vampire Killer. About Sanctuary, it surely isn't a thing by the era Lament of Innocence is set, if we are to take Awakening Under the Moonlight as canon (which I like to do), the medicine won't be made by Lisa until the age she was sentenced to death kicking off the events of Dracula's Curse. If we don't want to consider this bit of lore from the Takarazuka Act, we can't really tell who and when made Sanctuary.
The 64 games on the other hand are their own thing, so idk. The whip isn't even the same one, probably, nor there's been a Sara or Leon in the first place