For years up through the 1940's, the information is in book-ledger form. And they are BIG books. From about the 50's or 60's on, death and birth certificates were used, which are easier for the County to single-page xerox copy. If you want a xerox copy, you still have to buy the official copy from the county. Each different record counts as a new 'first' copy.
Additional copies refers only to exact duplicates of the first copy.
Different sets of information are recorded for births depending on the recordbook in use during a particular time frame. Sometimes the occupation of the father is recorded. For a while, the child number was recorded. In the 1940's, as part of a nation-wide effort to get all citizens registered in their county of birth, many additional delayed entries were made to the birth records for people whose births was never originally recorded. The name of the person giving the information and their relationship to the person in the birth record is also given.