Why was the definition of chiral carbon changed? Before 1984, the definition of chiral carbon was, 


  carbon atom that is attached to four different types of atoms or
  groups of atoms


In 1984, the definition was changed to 


  Any carbon molecule that is not superimposable on its mirror image.


Why was this change made? Don't both definitions mean the same or is/are there cases where the former is false. Preferably, please provide an example
The IUPAC definition of asymmetric carbon is still:


  The traditional name (van't Hoff) for a carbon atom that is attached to four different entities (atoms or groups), e.g. Cabcd.


The definition of chirality centre is:


  An atom holding a set of ligands in a spatial arrangement which is not superposable
  on its mirror image. A chirality centre is thus a generalized extension of the concept
  of the asymmetric carbon atom to central atoms of any element, for example N+abcd,
  Pabc as well as Cabcd.