Continuity query (Yes, I know, it's Scooby-Doo...)

I know continuity isn't a big point in Scooby-Doo, but I'd always understood that The 13 Ghosts of Scooby-Doo, Scooby-Doo Meets the Boo Brothers, Scooby-Doo and the Ghoul School, and Scooby-Doo! and the Reluctant Werewolf (Shaggy's 'Red Shirt Years') were set together in their own mini-continuity. I just watched Ghoul School and was surprised to see Dracula turn up. As I recall, Dracula gives no indication of having met Shaggy before when they meet in Reluctant Werewolf (the film that follows this one). How does that work? Also, is Vanna Pira from Reluctant Werewolf assumed to be Sibella's (Ghoul School) mother?

By the way, I'd love to see a crossover between Scooby-Doo and Hotel Transylvania (the series). Something along the lines of this movie would work - but stick a bona fide mystery in there this time.