Does FamilySearch Have It All?

In a word, the answer is no. There may still be more information elsewhere even in databases at FamilySearch that have images. One quick example is the Kentucky County Marriages 1797-1954. The description indicates that these entries are extracted from marriage registers, bonds, etc. Even in a county that appears to be "done," there may be more records. Mercer County's marriage register is included in the index-which is helpful. However there are also marriage bonds for that county which do not appear in Kentucky County Marriages, 1797-1954. Those marriage bonds are something you need to see. Only looking at the image of the register is not enough.