When houses were built a century ago, the use of trim around doors and windows, and between walls and floors was primarily a practical application.  Closing or covering the gaps between two different elements like walls to floors, the builder would use a simple flat wood board to create the base board.  Decorative elements, like a smaller piece of ogee, may have been added later to dress things up.  This smaller piece of trim additionally covered any gaps between the base trim and the wall. Remember, back then they did not have caulk to fill gaps.