This is kind of an out of the way subject, but there are previews on the DVDs, and I guess TV showings (all of them I guess from the original showings), that do what previews are notorious for doing, which is giving away the best parts. Which is especially aggravating if you're seeing the episode for the first time, or the first time in a long while.
Three of the most obvious ones (all from Season Two) are A STITCH IN CRIME, THE GREENHOUSE JUNGLE and DAGGER OF THE MIND. When it comes to the first two, I don't think I have to name the big moments they give away, since they're very famous ones among COLUMBO fans. With the third one, the preview gives away what's probably the best funny line of the story, and also a surprisingly scary moment.

At the other extreme, two of the previews that are done very well are the ones for CANDIDATE FOR CRIME and REQUIEM FOR A FALLING STAR. The first one misleads you in a big way about what you're seeing, but in a clever way. And the second one "juxtaposes" that Peter Falk line and that Mel Ferrer line in a pretty good comical way.

The one preview that always bothers me is PUBLISH OR PERISH since it shows two scenes that aren't in the episode. One where Eddie Kane says he'll be the expert behind every bombing in the world and the other shows Riley Greenleaf giving a salute and saying "Bombs away, Eddie Kane."

I guess originally that they planned to include the scenes but then decided later to take them out. But never adjusted the previews to account for that. That's the only thing I can come up with

Yes, that makes for fun watching! I like the previews, and I'm glad the DVDs have them. It's one of those now-forgotten features of TV shows, like (here I'm not referring to Columbo) the tail-end scene, a sort of one-minute encore that used to be common in comedies. They seemed made to be optional, so they could be removed for more commercials, although once in a while there'd be one that puts a whole new, final twist on the plot. Even the traditional opening theme song seems a relic now, for the most part.