Turn to the fourth page of the book--this is where the publishing dates are usually printed.
Look at the top of the page. You should see the name of the publisher and, next to it, a date: this is not necessarily the original publishing date, but the publishing date of that particular edition. Look further down the page and you should see--if this is not the original edition--another publisher name, date and country of publishing.
Take note of this date since it is when the first run of this edition of the book was published. If there is a second, earlier date printed then it means that this edition of the book is not an original, and that if the first date is not before 1950, then this edition was published after 1950 even if the second, earlier date is before 1950.
Turn to page 4 of the book, or the first page you come to with dates and publishing company names printed on it.
Take note of the date which is printed after the sentence that states, roughly, "This translation first published [date]." Be aware that this may not be the edition that you are holding in your hands.
Check the other dates--if there are any--printed after this statement. When "Reprinted" is written, followed by a list of dates, the very last, latest date will be the date of this particular edition. Otherwise, look for the latest date which has this edition's publishing company printed before it.
Turn to page 4 of your book.
Look at the list of short stories collected in this particular edition--printed next to them will be each individual story's original publishing date if they were published individually in publications. Ignore these because they do not indicate when this particular collection was published.
Look for the statement "Published in [publisher's title] [date];" this will be the date that this particular edition was published. If, however, there are later dates printed after this statement then the last, and latest, date will indicate this particular edition.