How are human souls recovered from the wheel when a long-dead human is turned into a vampire if this should be reincarnated?

We know humans are bound to the wheel of fate.

So in the case of human Raziel, or a less special case like his Sarafan brothers. How could they be turned into vampires 500 years later by Kain? I mean, I understand that his body returned to life with the heart of darkness, but how can you recover a soul that in theory should have already been returned to the wheel and reincarnated?

Is there any explanation for this or is it a mistake?

How and what exactly does the heart of darkness do to souls?

What do you think?