2, 3 and 4 July 1958
USA provided its own stamps, and a tremendous number of different cachet FDC covers are known. Based on the number of different philatelic items you encounter on the market, you can imagine that a lot of collectors went at the USA buidling at Expo 58.
Parodoxally, up to now, only cancellation of 2 July have been identified. However the American stamp and cancellation depict the FDC of 4 July. Even better, the cancellation used was covering up to the last day of Expo 58 being 19 October 1958.
The mixed cancellations are rare or unique.
Moreover, the only covers of Campo Rodan you would notice with the foreign stamp and cancellation were from the USA (see also below).
Official Expo 58 cover edited by Campo Rodan
The Official edited cover with logo of the country (edition is not identified)
Campo Rodan cover with American stamp and cancellation
Large cover with all Belgian stamps cancelled mixed with the American stamp
Set of maximum card with a Belgian stamp and American stamp with respective cancellations.
Unique stamp with the three first day cancels of the USA, plus the day cancel of the American stamp and official expo 58 label. RR
Large official cover with all 6 Belgian stamps
