Canon retconned, but also Dracula could have easily assumed his position/ power as "Sire"(as King of Wallachia) upon Vlad's Death starting the actual Dracula Legend.
I fully agree. Dracula's Curse happens in the year Vlad III declared his third reign (1476). He died a couple of months later. And I think the CoD manga implies he sent Hector and Isaac to "destroy the land he once protected" (or so says the Wiki. I can't be fully sure since I haven't read the manga).