it matters on bookcat because the various editions of the same book are listed as different editions of different books if the form of the title differs -
- unless the "english title" field is used to combine them; which ordinary mortals can't achieve other than by submitting a correction, once an edition's been added. (this comment is from another edition of this book)
Responding to a correction request, Wikipedia has the title as "The A. B. C. Murders". agathachristie.com, whose connection to the late author (or her estate) is doubtful, has the title as "The ABC Murders", omitting the stops. Which to choose? Does it matter? . . . Perhaps an entry for the original edition might resolve the matter.
<edit> FWIW, this 1936 Dodd, Mead edition as listed on ebay shows the title with stops. (this comment is from another edition of this book)