There's actually a way to get around the whole "such and such couldn't have fought Dracula because at the time Dracula was dead/sealed away/ on vacation in Tahiti" stuff.
There was a Hammer horror movie called Taste the Blood of Dracula where after Dracula was dead, somebody came along, gathered up his dried blood and ... well, you heard the title.
And with that, the person was transformed and Dracula was reborn.
So, let's say Dracula was dead/gone/whatever.
Assuming a similar effect, somebody could have got some of his blood, or maybe his eye or fingernail or something consumed it, and was corrupted by it turning them into ... not really Dracula, but a copy of Dracula, possibly a weaker or flawed copy. The real guy is still resting, but there's somebody else out there that's mostly Dracula, and may even believe themselves to be the real thing.