David Rumsey Map Collection, Map of the United States, 1809. Published by Abraham Bradley.
An ancestor lived in early Virginia which was subsequently divided into other counties and state. Assuming that person lived in the same home but the land was annexed to another state. Their birth would be, legally I assume, would be in that city, county state at the time. A few years later, the same piece of land ended up in an neighboring state. The census taker comes along and asks about place of birth of parents. If a parent answered the door, did they typically state the actual place of birth as it was known at the time or did they normally state what that place became?
Your response to your own question is essentially correct. When the U.S. Census was taken, most of the time, whoever answered the door was asked the questions and may or may not have known the true details. But your question brings up a basic rule of genealogy: places are reported as they existed at the time the event occurred. The reason for this rule is simple, genealogical records are most frequently accumulated geographically. So, the location of any event in an ancestor’s life will determine, to a large extent, where the records will be found.
There are exceptions, for example, local and county records could have been accumulated in a central repository, such as the State Archives. But recording information about your ancestors using present-day locations, may cause considerable confusion and result in an inability to find the original records.
In the above case, it is also important to note that people have a tendency to answer a question about their origin by reference to a place where they are “from” and not necessarily where they were born. Sometimes people say they are from a large city when the smaller suburban city is unknown. It is also common, even in the U.S. Census for people to provide inaccurate information.