To compliment Scoop's post showing the Project MOON adverts, here's the similar C21 spread from the trade journal Toys International from the same month [it wasn't earlier than Project MOON as I first thought but came out at the same time!]. It's prophetic how the word MOON appears here too. The writing was on the wall for C21 and there was of course that one small step for Man to tie into.
Regent Toys used these illustrations for their own ad, which presumably C21 agreed to when they got hold of their surplus stock.
Below is another trade ad where the brand Project SWORD was used by Century 21 [date unknown]. Its the same Zero X, Probe Force 1 and Cape Kennedy Set illustrations again. Note the T in a Circle logo on the snout of the Moon Bus, which featured in virtually all C21 Moon Bus adverts!