Q101 December, 2011   member 239   First Day Covers for Graf Zeppelin overprint

Most catalogues give the day of issue as April 6, 1931, i.e. Zeheri, Gibbons, Balian, Nile Post, while the Handbook gives no date but states April 6-11 for the visit. Sears give dates seen as 9/10 for cancels. However on the website the section of the Zeppelin flight shows examples for April 7 for Alexandria and April 11 for Cairo. When I made up a section on the website site for first day covers I left blank the one for this issue - based on the idea that a FDC should have the date April 6. Is it correct to say that the date of issue is April 6? And if so, are there any FDCs?

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