law: Court Fees Act, 1850 
  21.Effect of substituting or adding new plaintiff or
  
  defendant .-
  
  (1) Where after the institution of a suit, a new plaintiff or
  
  defendant is substituted or added, the suit shall, as regards him, be deemed to
  
  have been instituted when he was so made a party:
  Provided  that where the court is satisfied that the
  
  omission to include a new plaintiff or defendant was due to mistake made in
  
  good faith it may direct that the suit as regards such plaintiff or defendant
  
  shall be deemed to have been instituted on any earlier date.
  (2) Nothing in sub-section (1) shall apply to a case where a
  
  party is added or substituted owing to assignment or devolution of any interest
  
  during the pendency of a suit or where a plaintiff is
  
  made a defendant or a defendant is made a plaintiff.