> at what point and how did the exclamation point make it in
>the pali canon?

In translating it into English, I'd guess, possibly in connection with certain emphatic indeclinables. Ancient Indian punctuation is very simple, and there's nothing corresponding to an exclamation point or a question mark that I've heard of. It's just a bar | and a double bar || (hope the symbols show properly).

best regards,

/Rett