Thirty-eight of them begin with the word and.

I've always thought that particles like this were a kind of punctuation in non-metrical oral literature. Beginning a sentence with and or but indicates that one sentences has stopped: sort of a rhetorical version of a period (or full stop).

Also, how does one handle the sentences to be coordinated if they are distributed between two writers?

John said "Do not end a sentence with a preposition."

"But better writers than you did it all the time!" Mary replied.

Ceci n'est pas un seing.