Neither do I. I would be interested to learn any of the differences between the different lands. [Now for those tiers] The tiers are much like a pyramid. Purebloods, or Level A, being at the very top. They possess the most influence over the other levels and are the only ones that can turn others into vampires. The next tier, Level B, contains the nobles or aristocrats. C, are the common vampires. Level D is reserved for those who have been turned from humans. While they remain in control of themselves they remain in this category, without drinking the blood of their masters- the one who turned them, they are always subject to the possibility of dropping to Level E. The fall can be delayed if they are able to drink from another powerful vampire. Once they become level E-- it's the responsibility of the upper classes to eliminate them.

[The modern literature certainly would be a bit bizarre]

[Although he doesn't say it openly, Kaname finds that practice distasteful. He supposes there is no alternative while trapped in this place.] A pity there's no source for blood tablets here... [And at least the victims aren't destroyed]