In LOI only the Ebony Crimson and Philosophers stones are mentioned. The Ebony Stone I am assuming was worn by Walter and shattered when Leon used the Vampire Killer on him. The Crimson stone was wielded by Matthias who made Walter's soul his with the stones power thus becoming an immortal and a vampire.....BUT!!!!!
As quoted by Rinaldo it's the Philosopher's Stone that grants eternal life but bestows the wearer with the vampires curse. If it takes the other stones to make the Philosopher's stone Matthias should not be a vampire unless the rules of alchemy apply that I don't know about which is very possible. I know nothing about the metallurgic arts & I ain't no smithy per say but I am predisposed to a life of aimless wanderin'. And cue the BlueGrass with guitar accompaniment.
The Philosopher's Stone grants 'eternal youth' according to Rinaldo. The Philosopher's stone does not bestow the curse of the vampire to the wielder, that is the Crimson stone only!
Rinaldo Gandolfi: Making the Philosopher's Stone is the ultimate goal of alchemy... It provides eternal youth. The two other stones were apparently created accidentally. No details of how they were made remain now.
Leon Belmont: I see... I know about the Ebony Stone. What kind of power does the Crimson Stone have?
Rinaldo Gandolfi: I don't know the details. It turns the souls of vampires into power for its master. These two stones are the vampires' greatest treasures.
Leon Belmont: Wouldn't the Crimson Stone work for humans as well?
Rinaldo Gandolfi: If all it gave you was power, that might be so...
Leon Belmont: What do you mean?
Rinaldo Gandolfi: I've heard that it bears the curse of the vampires as well.
Leon Belmont: I see... So humanity would be lost.
Rinaldo Gandolfi: There are no greater treasures for those who become vampires.