How likely is this? Passport Description in Novels

Some of my recent reading:

• Sayers' Clouds of Witness
• Christie's There is a Tide, aka Taken at the Flood
• Christie's The Secret of Chimneys
• Christie's So Many Steps to Death, aka Destination Unknown

 Maybe i'm making too much of this, but
all of these have, to a lesser or greater extent, characters assuming the identity of someone else.

Design?

  Usually it's by design.  So Many Steps to Death (spoilers here!) begins with a suicidal redheaded woman being recruited to assume the identity of a red-haired woman whom the Secret Service is following, killed in a plane crash. (It's pitched to her as a more sporting way to go out.)
 In Chimneys (spoilers here!), the first chapter contains an account of two characters arranging for one to travel on the other's passport, the descriptions and even blurry photograph being similar.  And there are many more identity surprises throughout the novel, some characters going by several different identities.
  There is a Tide also contains characters deliberately masquerading as someone else. 

Mistake?

  In Clouds of Witness, however, the situation is a little different. This book is concerned with a trial, with witnesses required on each side.  One of them is sought out based on a "passport" type description, but this is a totally different person, though giving useful evidence all the same - to the other side!


You also might like https://ahsweetmysteryblog.wordpress.com/2016/11/22/coming-home-two-examples-from-agatha-christies-post-war-england/
even if you only look at the marvelous cartoon at its beginning.