Bakers percent.

I am planning on mixing up P. Reinhart's SF Sourdough from C&C and have a silly question relating to Baker's Percentages.

I have a spreadsheet set up that I use to convert recipe's to grams and scale it to my needs. In that spreadsheet, I breakout the starter into its flour and water content to figure hydration percentages. I also figure Baker's Percentages. My Baker's Percentages do not match up with Reinhart's because his are based solely on the main flour ingredient in the final dough and he does not account for the flour in the firm starter, whereas I do.