OK, so how did the book Martha wrote survive both the fire and 118 years of existence? (No acid-free paper back then.) Both are answered simply that it was locked in a safe. Martha locked it away, intending to open the safe and retrieve the book from the airtight safe when Mavis reached her 118th birthday. After the fire, Dracula went back to see if there was anything salvageable and found the safe with the book inside. Either vampires have a magic that allows them to unlock things or he just knew the combination.
"You only zing once!" Is the reason why Dracula finally goes after Johnny. Fridge Horror kicks in when you realise that since he already zinged, and presumably lives forever, he's doomed to a literal eternity of loneliness. Explains a lot about both his hatred of humans and his rabid protectiveness of Mavis.
On that note, it is basically implied at two or three points through out the film that Johnny is going to become a vampire in order to stay with Mavis, this may be a case of getting crap past the radar....
One related to the game on the Nintendo 3DS: Why the hell are the hotel staff and monsters attacking Mavis? Worse yet, this can even happen in plain sight of her own father and friends, and none of them would lift a finger to help you.