Given that the 100th person sees hats 0 to 99, the 99th sees hats 0 to 98, and so on, with the first person seeing none, what is the maximum number of correct guesses possible?

With 100 people in a line, the maximum number of correct guesses is 99. The first person, who sees no hats, cannot deduce their own color and may be wrong. All other 99 people can use the parity strategy to determine their hats exactly. Therefore, 99 out of 100 guesses can be guaranteed correct.