Each FDC can be found stamped with perforated or imperforated stamps. I did not multiply the number of images below, but you will find as much as both type of covers.

FDC covers of stamps with cancellation of 17 April 1958 (only two "official sets" to be known - no editor known):

Set 1:

Set 2:

Set of FDC for the souvenir sheet (only 1 cachet known):

On 9 December 1958, another souvenir sheet has been sold to the philatelic market during the "Congrès de la Fédération Internationale Philatélique - F.I.P." at Brussels.