When looking at deed indexes, be sure to look at both the "Grantor Index", an index to those selling the land and the "Grantee Index", an index to those buying the land.
To find a birth date from a death date, subtract the age in years, months and days from the date of death. This is a very close approximation.
Marriage Records may only be records of the wedding. However, you may also find the Application for Marriage completed by the bride and groom-to-be. Marriage records may also be corroborated with church records. Check everything for correctness.