Book from Black's house

[B.G.]

No: HPFGUIDX 129683

I've read OOP a couple of times but it took listening to an audio CD 
to bring my attention to a little clue (perhaps).  I tend to skim 
paragraphs sometimes - one just cannot afford to do this with HP 
books.  When they are cleaning the Black House, Sirus used a book to 
swat a creature off of Harry.  This book was titled, "Nature's 
Nobility:  A Wizardry Genealogy".  Why would JKR mention the title?  I 
think Harry will remember where he saw this book and use it to uncover 
the HBP.

I still think that Draco is not pure blood and that is the main reason 
his mother did not want him going to Durmstrang.  Durmstrang's 
application process might have revealed that her line is not as pure 
blood as she has led Malfoy to believe.