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 That date of "1957" is not a date of publication; it is more likely a date of composition (which the site tends to use more than dates of publicationsee below).  The play was published first in 1958 in a literary magazine (Encore) and subsequently published by various publishers such as Methuen (in the UK) and Grove Press (in the US), in various revised editions.  One needs to do more advanced research to make such distinctions among possible dates of composition and dates of publication accurately.  Pinter's works have a very complex compositional and publishing history.  Please see the "Bio-bibliographical Note" hosted on the Nobel Prize site for related critical resources if one wants more accurate information than is currently in this Wikipedia entry.  The entry still needs substantial revision and editing.  

Cleanup
[I'm adding a cleanup tag on the article.]
Dates on Pinter's website often tend to be dates of final composition and/or dates of first performance and not dates of first publication and/or dates of (film/tv) release.  (Several sections of his website were compiled by research assistants tasked with such work and by his (multiple) assistants beginning in around 2000, when the website was launched.  There are sometimes typographical and other errors in the sections.)  Some works were published long after they were first written; e.g. his novel The Dwarfs.  When not confusing, one tries to use those dates or clarifies discrepancies otherwise.  Did some cleanup of this article.  Added some citations and additional sources for verification and further reading.