Every time a Collection is added to FamilySearch.org's Historical Record Collections, there is a page/article created in the Research Wiki describing the collection in detail.
The key to the older images, in the past, has always been the Family History Library Catalog, the main catalog to all the microfilms.
FamilySearch and BYU are digitizing family history related books from their collection as well as from other libraries. These books show up in the Family History Library Catalog as available online.