All existing municipalities which were incorporated or which changed their corporate organization under “An Act to provide for the incorporation of cities and villages,” approved April 10, 1872, as amended, and all existing municipalities which were incorporated under any general act prior to July 1, 1872, shall be treated as properly incorporated under this Code.
     All municipalities incorporated under any special act in effect prior to July 1, 1872, which at the date of the passage of this Code are still functioning under the special act which created them, shall remain as properly incorporated under that special act.