Czech Republic and Slovakia postal administration issue on October 2, 2023 a souvenir each at the occasion of the 30th anniversary of establishment of their postal administrations. This identical souvenir sheet shows the particularity that for one country the stamp with denomination is the label of the second country, and vice versa. This type of, still considered as a twin issue, is described under type [T4] in Volume I of the catalogue, and was observed already in the past with e.g., a joint issue involving Jersey and Guernsey [T19941001]. These souvenir sheets and stamps are also available as mixed covers.

The mixed FDC card proposed by the Slovak Post is in fact made of the strip of logos and stamp from each country (taken from the souvenir sheet) and first day cancelled from each country. Slovakia issued 60,000 samples of the souvenir sheet, but Czech Republic only 30,000.