There have been two sets different maximum cards.

The first set is based on normal postal cards. The second set is based on the same design as the Official FDC Covers. However, you will find much easier the first set of cards with other cancels on it - like the one with the Benelux Building - mostly cancelled with the Benelux cancellation. The only exception is the Telexpo maxi card = it is always cancelled with the FD of the opening of the Telexpo Building - see Telexpo under Belgian cancellations > Other for more information.

 

The second set (of which I have only identified five of the six existing ones - the only missing one is this with the Atomium on it) is edited by Campo Rodan and has the same image as used for the Official First Day Covers, also notice the different days of cancellations. You also will notice that the ethic of the maximum card has not been applied here, since the stamp is each time the same, and should have been different (representing the image on the maximum card).

Hereafter you would notice a set of five maximumcards in the same Rodan design - these are much harder to find. It looks like the card with the Atomium is not existing in this serie.

Many other maximum cards have been published, but on other postal cards. The most known are the stamps with National Day Cancellation on the EGICARTE series.