@ CCComics:
The newsstand theory seems improbable to me. For one thing, Thundercron showed us a scan of a newsstand edition, and its UPC area is notably different from the UPC area of the comic he is asking about. For another thing, UPC barcodes on newsstand comics consistently (like, from 1976–2013 consistently) have two digits in the rightmost block, not the five digits in Thundercron's example.
@ Thundercron:
Thanks for your kind words. I enjoy looking at these oddball items, and trying to properly categorize them, but ultimately I am relying on the same observations and inferences as everyone else.
The cardboard-packaged multi-packs I am thinking of might be the "fancy, prestige collections" you referred to, or they might be of the entrepreneurial variety you mentioned. I really don't know. The impression I got from a brief examination, months ago, was of professional printing and packaging, but I can't say that I specifically remember a publisher's trademark on the package.
However, I do recall rather vividly another case that suggests (to me) that DC engaged in innovative retail packaging. Some years ago, I dated a fan of (among other things) Bugs Bunny. After hanging around me for a few months, she started collecting Bugs Bunny (and other) comics. One day, she came up with this one:

I was surprised because I didn't know it existed. It was clearly not a newsstand comic (no UPC, no color banding on the top edges of the pages). And I didn't remember seeing it offered by DC via direct sales (I think I even checked old Previews to verify; it was never listed). If it wasn't a newsstand comic, and it wasn't a direct sales comic, then what the hell could it be?
In time, my girlfriend located the other two issues in the series. We both examined all three issues for clues. Nada.
Finally, years later, she spotted an auction on eBay for a package containing two comics, of which one was an issue in this series. IIRC, the other was a Batman prestige comic, possibly Batman-Spawn. The eBay auction talked about "original packaging" and such. Taken at face value, the description in the auction accounted much better for the existence of the Bugs Bunny Monthly comic than anything else my girlfriend or I ever came up with.
You may not regard this as proof. Truth be told, I might be a little skeptical if I were hearing this from someone else. But for me, this is reliable evidence that DC engaged in non-newsstand, non-direct marketing, and it's not much of a stretch for me to think that Marvel might have done so also.