If you look at the upgrade page for Logos 5 <http://www.logos.com/whylogos5?>, reason 17 says, "These discounted books may not be available later." Under that section, it says some books get removed when they create new base packages, while others get added. It also says they removed many of the books from Logos 4.
Additionally, on the product page for the "Starter" package <http://www.logos.com/product/24531/starter>, there are several comments from people saying they are missing books from Logos 4.
Does anyone know if that is the case when you upgrade, or will you be able to keep all previous resources?