I searched for "Pinball Fantasies" with no matching games found. Via the wishlist comments I found it as part of "Pinball Gold Pack", so I would expect that in the search results.

I don't know how many packs are affected, that contain games with different names. But I almost did not buy it, since i thought it was not available ;)

If you just scroll down for a sec, you'll see "A great bundle with classics like Pinball Dreams 1 and 2, Pinball Illusions, Pinball Fantasies/Pinball Mania". Gog usually provides info about its packs in the description of the game.

Jep after I found that pack manually, I saw what is included. Thats good. But the search does not find it, when you type in e.g. "Pinball Illusions".

As far as I can tell the search box works on game titles, genre tags, and developer/publisher tags.

Some titles on GOG are compilations that include other games which may have different titles. Since the search box doesn't scan the game description (where included games are typically listed), something like Pinball Fantasies won't come up since the game pack's title doesn't include 'Fantasies' and that term isn't tagged anywhere for that title.

Another affected game was Incubation which is part of the Battle Isle Platinum compilation and nothing showed up when just searching for Incubation. They solved the issue by adding "includes Incubation" in brackets to the pack's name.

Guess they might do something similar for the Pinball Gold Pack but there's probably just too many different games in the pack to mention all of them in the title. Plus Pinball games probably aren't popular enough for GOG to take this case particularly seriously and Pinball enthusiasts are probably willing to investigate each of the Pinball games/packs available in the catalogue or look for a particular Pinball game by other means (as you also ultimately did). I for one instantly checked the Pinball Gold Pack when I first saw it, hoping that it would include Dreams and Fantasies - and obviously it did.

The weirdest one is that Planetfall is randomly in the Infocom Zork Anthology pack (but not Stationfall)
-one for all you 80s IF fans, there