There are differences between the two cartoons on the back of the coupon.
Firstly, the carpet is colored grey in one and not the other. I presume this is because perhaps early Xerox machines didn't color solid colors in order to save ink?
Secondly, there are dots and lines in one cartoon and not the other. Is it possible that the same cartoon, but with modifications, was syndicated across several different magazines?
At a stretch, could the CIA/FBI have got hold of one of the versions of the magazine that was sent away for copyright, and it is the coupon from that that they used to purchase the pistol for Oswald and then the magazine subsequently printed the cartoon different in the actual copies they put on newstands than the one they sent off for copyright?