The 1972 revision of the Copyright Law extended the copyrights dated
after 1906 for a period of 75 years following the original copyright.
What this means is that in 1992, films made before 1917 have fallen into
public domain.  This rolling date will keep up until the old copyrights
are no longer in existence.
As always under the copyright law new elements of a work based on an
underlying copyright are themselves copyrightable.  Thus if you want to
to a remake of 'teen years Chaplin films you may do so and copyright the
new work.  BUT so can anyone else as long they work solely from the now
public domain material.
Cal Pryluck                               <[log in to unmask]>
Dept of Radio-Television-Film             <PRYLUCK@TEMPLEVM>
Temple University
Philadelphia, PA 19122                    voice (215) 247-9663