These explosion backs occurred in two different years, 1983 and 1987. In 1983, the characters of Trip Wire, Torpedo, Major Bludd and Destro were exploded out. I recall that both Trip Wire and Torpedo figures were almost non existent until the late summer of 1983. So, they might have been a case where Hasbro didn't want kids looking for them until they were released. Destro and Major Bludd are, likely, the same thing. Destro's look was some of secret until his full appearance in the comic. They hinted at him, but didn't show him for a few months. Bludd, though, was a mail away. So, any kid who collected Joe was aware of him. But, his carded figure may have been delayed until the mail away was done, so he was blocked out, too.
The reasoning behind the coming soon explosions isn't fully known. In the case of Kenner's Star Wars line, Lucasfilm specifically didn't want anyone to see the Ewoks (or Jabba the Hutt) prior to the release of Return of the Jedi. So, they were blacked out on the earliest cardbacks. (I got a Chief Chirpa figure that had him still blacked out on the back.) But, G.I. Joe didn't have a movie to spoil. (Well, it kind of did in 1987. But, the most prominent movie characters like Falcon and Jinx are showcased while other, more obscure characters are not.) It could have been that the artwork wasn't ready at the time when the cardbacks were done. But, this seems like an unnecessary rush.
In December of 1986, my mother took me to Toys R Us. While I always looked at the Joes, I didn't figure I'd find anything really new. But, among the carded figures were newly released 1987 characters. I bought Falcon and Cobra Commander. I have no memory of who else they might have had on the shelves. It is likely, though, that because the 1987 figures were seeing a slightly early release for the 1986 Christmas season, Hasbro saw an opportunity to bring back the explosion backs.
Explosion backs are rare. MOC examples are very pricey and can be ridiculously expensive if you find a highly desirable character on one. Even loose explosion back cardbacks can be tough to find. But, once you have one, you kind of have them all for a given year. To me, the interesting part is the inconsistency of Hasbro's usage of them. Why just those two years? Maybe they didn't test well either time and were never brought back. Regardless the reason, they are a footnote in Joe's retail history.