Final answer:
The phrase suggests the stories were found among the papers of the late Diedrich Knickerbocker, a fictional historian created by Irving to provide authenticity and context to his tales.
Step-by-step explanation:
The phrase "This was found among the papers of the Late Diedrich Knickerbocker" serves a specific literary purpose. Washington Irving used this fictional attribution to create a sense of authenticity and historical perspective. By implying these stories were discovered writings of a deceased historian, Irving lends credence and a contextual background to the tales he presents, particularly in works like 'The Legend of Sleepy Hollow' and 'Rip Van Winkle'. It's a common narrative strategy known as a frame story or a false document technique, which was quite popular during the era in which Irving was writing.