A lot of unanswered questions as well. To name just a few:
>What was the whole deal about Alucard being locked up in the basement for a long time? Did Arthur feel like he was too dangerous to utilize? What is the timeline here?
>How did Millenium get Mina, and was she alive at the time? She was only 19 when she encountered Dracula. Not to mention, she never turned back in the Hellsingverse. So how did that even turn out?
>>158835892
He was locked in the basement because there simply wasn't any threat after the Nazis that warranted using him. With the advancements in firearms, Hellsing's foot soldiers were able to go toe-to-toe with whatever cropped up. Why bring out a monster when you have a man to do the job? As for Mina, it's not really explained. Could be that she was rounded up during the German campaign in Romania, found surviving mortal wounds, and shipped off to the Major but it's all just theory.
>>158835892
To dangerous for the first one, mina was sort of turned back but the dracula curse was still in her.
Hence why all of the millennium vampires were hacks or 2nd rate vampires, they were using a sliver of the curse that survived in her.