Ok, there are probably more “pure bloods” out there but what exactly is the difference or significance of a “pure blood” in contrast to an ordinary Vampire? Frankly the “revelations”, if you want to call them that, that we learn about Vampires makes things more confusing and outright contradicts what we already know. More questions than answers. Can we really accept this as real and new lore considering the way Vampires have been handled and Skyrim’s other issues? Are the Vampires in the castle even Volkihar? It just seems to me that we are all grasping onto different pieces or lore new or old and filling them with speculation. Thoughts?
The only different to a "pureblood" and a "thin-blood"/"turn-blood" vampire is that they were given vampirism by the creator. We all know Lamae wasn't only the first vampire, but also a pureblood.
Honestly, I like the pureblood idea. Ever since I had my vampire characters in Oblivion and in my stories, they were pureblooded, though I left the actual reason vague and only said they were effected by a Daedric Pact with Molag Bal. And that was it. Fortunately, this seems to be the case as it is made official in canon. Pureblooded vampire do not really contradict lore at all, we had an "almost" pureblooded vampire when the Grey Prince was born from a vampiric father and a mortal mother. So the idea of a vampire not being turned by another vampire is not exactly far-fetched.
Now, I do agree with you on the way vampires had been handled in Skyrim compared to other lore. For example, we could blend in if we fed on people, which is a power unique to the Cyrodiilic vampires(made unique not from the book "Immortal Blood" alone, but the "Manifesto Cyrodiil Vampyrum"). Bethesda somehow fixed this with the new DLC by making all vampires obviously hideous with glowing eyes, pale skin and fangs, bat-like nostrils which serves as proof other vampires cannot blend in as well as the Order can. And while NPC's won't attack players regardless of stage, you can bet in lore they are shunned and attacked for their obvious vampirism.
"Can't you tell just by looking at me? I'm a vampire."-Serana.
"I do not work on dead flesh."
So it is obvious people can tell your vampirism, and we can safely assume that the "Volkihar" do not have this ability. Now, on Harkon and his family, we know they live in Castle Volkihar. But other than that, none of them call themselves Volkihar or even mentioned the ice-breaking ability and etc. We're left in the dark on that matter, but I suppose Bethesda slapped on "Castke Volkihar" to further convince fans that Harkon and his people are from the clan. But I agree, they are just molding things into one.