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| WWII Prisoners Of War Series |
| Vatican Radio Issue |
| L'Osservatoree Issue |
| World Fair at Brussels |
Your answer was: World Fair at Brussels. |
Answer: According to "Vatican Notes, Jan/Feb 1958, Vol 6, No. 4, p. 2", Vatican City issued its first 'non-religious' event stamp for the 1958 World Fair at Brussels for the first time in its twenty-nine-year philatelic history. |