Inspired by some other old posts tracking FAKKU release rates (including a lot of sadly-deleted spreadsheets) I spent a little time going through comic issues to see what material was never released at all. I generally didn't include any missing stuff from around the last year or so since there's a bit of a long tail where the last few bits of an issue take a while to come out, but they do usually make it out
eventually.
I also didn't really consider any of the bits of things that FAKKU
never releases like ads, filler pages with the comic logo, tables of contents, and so on. The point was more to list all of the things that normally get released, but never did.
In Kairakuten 2016-02 through 2016-05 there was a "from the archives" story that was included as part of a Kairakuten anniversary thing. One could argue that they shouldn't count, since the were re-releases from much older issues and not truly a part of the issues FAKKU was releasing...but in the 2015-06 through 2016-01 issues FAKKU
did include those re-releases. Not quite sure why they stopped.
The final "Cover's Comment #195" in Kairakuten 2019-07. This specific one was a bit of a weird one since it was less of a behind-the-scenes on the 2019-07 cover and more of a two page retrospective of on Range Murata's covers, but it was still a Cover's Comment so it seems a bit weird to just not release that one. I guess this one also technically violates my "only older than a year" rule but it stood out to me because FAKKU has released a bunch of "Cover Girl's Episode" (which replaced "Cover's Comment") since then, so the gap stands out.
The sketch half of the pin-up art in X-Eros #44. This was something usually included in other pin-up art releases, but not in the #44 one.
Sayori's story from Shitsurakuten 2016-05. AFAIK this was technically was released at one point but then got pulled over rights issues, so I don't really expect that to come back. Which is disappointing since unlike the other things I'm listing here it was an actual story (and a full-color one at that!) but I guess there's not much one can do but be sad about it.
Pin-up art from Bavel 2017-10, 2017-11, and 2018-02. Now, these were special cross-collab pin-ups and not the usual ones, but some of the later releases (for example
https://www.fakku.net/hentai/anim-x-bavel-special-bonus-pin-up-by-narumi-suzune-english) did include them.
And that's all I could dig up. There's other occasional bits one could argue they should include, for example there's sometimes extra story preview pages which kind of straddle the border between being an advertisement and being a part of the story. But I just tried to stick to the things that are normally released but never were.