I am interested in the Hermeneia commentary series, specifically the book on Matthew 1-7. I cannot afford to buy the whole series and would like to buy books as I need them. Is it possible to do that with Logos or must I buy the whole set? Also, I see that you offer an upgrade containing the portion of Matthew that I am most interested in for $90.00. Can I simply buy the upgrade or must I already have the original set in my library?