This is not 'SNL: The Best of Steve Martin' from 1992

I see that at least one reviewer has confused the two. They have the same title, but the one from 1992 is a VHS that's probably never been released on DVD, and it probably never will. And that's just as well because it actually only contains edits of two episodes, 3x18 (1978) and 5x01 (1979), back to back. As noted by that reviewer, it leaves in a couple of segments where Steve doesn't even occur, like Weekend Update and performances with The Blues Brothers. Of course these episodes can now be found in complete form on the full season DVDs.

The newer one, from 1998, is a DVD release. I haven't seen it, but it's apparent that it contains other sketches, from more episodes than just those two.