23 till 31 August 1958
Precancel stamps exists already a long time, and are issued by numerous countries, hence you had organisations which were created in order to cover this type of stamps. More can be read on the website The Precancel Stamp Society's.
Officially, the following has been said about the first and only international philatelic exposition during the Expo 58: "The Belgian Association of Precancel Stamps has decided to set up the first European Exposition of the Precancel Stamps in Europe. This exposition will offer the nicest precancel collections of the UK, Germany, France and Belgium. The Expostion with free entry has got its venue in the Building of the European Council, because of its European approach. It lasted from 23 August till Sunday 31 August 1958. An official Congress, accepted by the Expo 58 organisation, will group on Saturday 30 August, the most important collectors and specialists. The President of the Congres was Dr. W. Engelhardt from Berlin. During that day, 30 August 1958, a special cancellation was issued in the same building." (hence only cancellations with that day can be found).
Unofficially, the following was said about this exposition and Congress: It was not a success. The PRECANCEL STAMP SOCIETY of Great Britain was present with three of its members: a Rev West with a display of Austrian Newspaper Wrappers, Mr Higby showed French Precancels and Dr Englhardt with rare precancels of German, Roman State and Finland. Strangely enough though, in total only 12 members were present but despite this a wide range of displays were exhibited.
Philatelicwise, you can find quite easily the second edition of the Campo Rodan FDCs on the market, which is getting more difficult are the first edition FDCs, and others.
Official Expo 58 covers (first and second edition) edited by Campo Rodan.
Official cover with cancellation. (R) (edition is not identified).
Official Expo Card cancelled.
Cover with double cancellations with the European Council in Strassbourg. See also more information about this
Finally large cover with the full set of Belgian Stamp, cancelled
