I do not think it is literally blood because what really counts is power/spirit, blood is just the vehicle. When a child is born it is not just the dna that is combined, it is the soul and spirit too. I think that is the traceable stuff for the spell. Bloodline is an old metaphor so I do not think we have to take it literally.

A forgot to mention Maggie. But what would have happened if Harry had returned in a different body? Like corpstaker planned and Kemmler did a few times?

Few things.

I do think blood is the medium, much like hair or fingernail clippings.

My WAG: Harry isn't even aware he's juicing the curse, and Thomas is the link. Harry has always had this power drain he was unaware of and doesn't notice, passed via Thomas via their blood link, and from Thomas to Lord Raith.

My other WAG: She didn't stop his feeding. She amped up his anti-magic aura to absorb any spiritual energy he tries to eat.

EDIT: OOOh, or it feeds Thomas instead

Does it have to be "gifted" . I assumed magic using mortals had the capability to use it, but some just need a push. I mean it runs of their own soul.

Gifted. Per WoJ, only about 6 wizards have ever been granted it.

It's the angelic analog to Hellfire.

Uriel is explicit about having gifted it to Harry.

Maybe, but the Red Court might just not have been that interested. The population density in pre-Columbian times was way higher in Mesoamerica than in North America north of Mexico, really pretty amazingly high given that they were doing all their agriculture without draft animals or anything.

And the Red Court probably avoided the overly-sunny and thinly-populated desert of northern Mexico; they would try to expand southward rather than northward.

Higher or not, territory is territory. There's the question about whether the supernaturals could reach to the New World via the Ways or not.

I wouldn't be surprised if she was 1,000 years old. Is there anything form outside the novels and short stories on her age?

Yes. Ish.

Papa Raith paints portraits of the mothers of his children. The oldest portrait is from, I think, the 16th century.

The Blacks are new, relatively speaking. Starting around the time of the Conquista if Dracula was the first.

The White Court, which uses Etruscan as its official language, quite probably was the original "European" vampire. Maybe they were originally behind Roman patricians? Their move to eliminate the Black Court makes more sense if the Black Court was encroaching on their territory.

Their moving to North America is their expanding operations.

In fact, I have this complicated and longwinded theory that to understand the first half-dozen Dresden books, you have to view Chicago as a kind of supernatural Casablanca that both the Red Court and White Court were making power plays to take over; and Harry wandered in before Marcone "stole" it as a Freehold. Too valuable of a nexus.

I assume Harry is a Hades figure- an Erlking holding the leashes on the Furies.

He is a figure of just retribution, a towering pillar of bad news for those who transgress and merit his wroth- which means the relatively innocent (Mrs Sells) would feel reassured, the sensitive (Molly) would feel for his loneliness, and the wicked would feel threatened.

And the gentle (Bradley) nauseated.

Observation:

Among the Fae, height indicates power.

WAG:

Harry's mother spent a lot of time in the Nevernever while pregnant. Benefit: It enhanced Harry's power and incidentally made him taller.

Intent: She was targeting his birthtime exactly by using a mix of slower-time and faster-time locations. Thomas was the dry run, hence his birthday on exactly Valentine's. By changing her subjective timeline relative to objective time, she could ensure Harry's birth at the optimum time to produce a starborn. Side effect: He's tall.

The huge werewolf population of Chicago would argue otherwise. They are Paranetters which means minor talents, for vanilla mortals the only option is Hexenwulf.

Cite, please. This is intrepretive fanon. Alphas never said to have talent- they wanted involvement