Vital records and event information are more reliable when they are recorded near the time of the event. The longer the time from the event occurrence that the record is made, the less accurate it may be based on the memory of the person involved.
The 1940 Census lists answers to several new questions never asked before including where they lived in 1935 and what was their income for the previous year.
When the head of the household is no longer listed, don't assume he/she is dead. It's possible that the former head of household is now living with one of the children.
A person who dies "intestate" dies without a will.
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. There could also be a newspaper account of the wedding.