Citing different web pages by the same author in APA
The issue is that in APA style the author and year are used in the in text citation keys and these keys need to be unambiguous. When you have the same authors, in the same order, and the same date of publication, you add a letter to the publication date. You do the same thing even when the publication date is unknown. According to the APA blog


  Also remember that if you have two or more “in press” or “no date”
  references with the same authors in the same order, you should use
  lowercase letters—a, b, c, and so forth ... The only difference between these types of references and references with publication years is that “in press” and “no date” references contain a hyphen before the a, b, and so forth:
  
  American Speech-Language-Hearing Association. (n.d.-a). The knowledge ...
  
  American Speech-Language-Hearing Association. (n.d.-b). A strategy to ...
  
  Schafer, G., &amp; Plunkett, K. (2011a). The power ...
  
  Schafer, G., &amp; Plunkett, K. (2011b). Task complexity ...
  
  Schafer, G., &amp; Plunkett, K. (in press-a). The rapid learning ...
  
  Schafer, G., &amp; Plunkett, K. (in press-b). Sometimes a child ...