Some time ago, in an article I wrote, there was a question that listed the birth date of a child, but had no actual marriage date for the parents. Suggestions were made about how to estimate that marriage date. In response to that particular subject, I received the following comments from another researcher:
Further to your comments, it is also false to assume that just because a first child was born in 1850 that the parents were married in 1848/49. They could have easily been married before those years, during 1850 or after the first child was born. In an ideal genealogical world, people were married two years before the birth of their first child, gave their children their mother's maiden name as a second name and never moved from the area they were born in. - Elisabeth
Estimated marriage dates may not be as close as we would like.
Assumptions May Lead Astray
This brought up an interesting point. Many a time we will estimate dates because we cannot find them. We assume many things that may not be true. One of them is assuming that a couple married the year before the birth of their first child.
I myself have discovered in one of my lines a propensity for the first child being born about three months after the wedding. This happened for three generations of that particular line of my family. My own first child was not born until three years after the marriage. Neither of these examples coincides with the assumption mentioned above.
Are You My Mother?
Another assumption that can sometimes prove false is that the wife you know about was indeed the mother to all the children. Many times the wife would die and the father would remarry. This happened often in the 1800s on back.
These were tough times that required a mother in the household to do the cooking and other essential daily chores as the father was out plowing the fields or taking care of the livestock. So if the wife died young and there were small children in the house, it was not unusual to see him remarry.
Sometimes this is obvious, especially when the age of the new wife is so young that she could not possibly be the mother of the oldest child in the house. Other times it is not so obvious. And don't get sidetracked with the pre-1880 census. With no relationships listed, you cannot assume that all the children in the household are indeed the children of the head of the household.
Whenever you are following the trail of your ancestors, it is essential that you keep an open mind to all possibilities. Otherwise the very clues that you do find will not be recognizable to you because you will not see them.