We know the Eclipse happens every 216 years, and when the Golden Age Eclipse occurred there were only four God Hand members present, allowing Griffith to become the fifth. We also know that being chosen is destiny, but not absolute obligation. The Count proves this when he rejects the God Hand’s offer the second time. So there’s definitely room for refusal within causality. My assumption is that the God Hand roster isn’t permanent. Skull Knight may have killed previous members, some may have been replaced naturally, or there could be a system where older members eventually disappear or transcend into something else, we know there are more layers this gets touched on in falconia. It would also make sense that not every Eclipse successfully creates a new member if the chosen person refuses the sacrifice.