Why does my sourdough hydration math from 'The Bread Baker's Apprentice' fail every time?

I'm getting consistently dense sourdough loaves using the hydration calculations in 'The Bread Baker's Apprentice' chapter 12. The book specifies 75% hydration for the final dough, but when accounting for the 100% hydration levain, the total water-to-flour ratio ends up closer to 68%. Is this a rounding error in the text or a fundamental flaw in the formula?

Details:

• Levain: 200g (50% flour, 50% water)
• Final dough: 500g flour, 375g water (75% hydration)
• Total water: 250g (200g from levain + 50g from final dough?)
• Total flour: 700g (200g from levain + 500g final dough)
• Actual hydration: ~35.7% (250/700) ???

Am I miscalculating the hydration when accounting for pre-ferment? The book explicitly states to ignore the levain's water when calculating final dough hydration, but that seems mathematically inconsistent. Has anyone else noticed this discrepancy or have a formula that accounts for pre-ferment water? I'm ready to burn the book and start a new hydration model from scratch. 🔥