Ive encountered a few books from this series, and v7 is the only one that hasnt given me a skill increase of somekind....also it is worth significantly less gold than the others ive acquired...does anyone know why this is? Is it a bug, or just how its supposed to be? If thats how its supposed to be it doesnt make any sense....why should one volume of a 12 book series be worth so much less than the others? Why doesnt it give you a skill like the others? not a big deal, just very odd to me.

It is probably how it is supposed to be.
It is likely that there is a set number of skill books in the game, for example ten of every skill.
What book to assign a level up too is a bit arbitrary as there are such a lot of books, though it usually has to do with the skill.
In Morrowind the book increased mercantile, a skill that unfortunately no longer exists.
It is possible that they already had enough speechcraft books, which is the closest thing to that.
Anyway, it having a lower value pretty much proves that it is intended, as all skill books have a relatively high value.
If it is a bug it is unlikely that it would affect the price as well.

P.S Great story in those books, isnt it?

im reading them on UESP now

This is probably a mistake. In both Morrowind and Oblivion "2920, Sun's Height" increased Mercantile. I see no reason why it shouldn't increase Speech in Skyrim.

It's as designed. It's probably the most easy one to acquire as Urag gro-Shub always has this book for sale.

I am pretty sure that Sun's Height v. 7 is intended to be the most common book of the series. It was in the cupboard in Helgen keep at the beginning of the game for me. It was the 5th container I had ever looted. Extremely common book.