I'm currently working my way through the tv series Supernatural (currently on early season 5, watching via Netflix Streaming). One thing that strikes me as odd is that at the end of some episodes, there is a preview of upcoming episodes (e.g. S5E5). The word 'Soon' appears and then the preview scenes play, then the episode's end credits roll.
As I'm watching via Netflix, I assumed I was missing some context here, like these were mid-season breaks. But, looking up this latest episode where there's a preview, there wasn't a mid-season break at this point in the season, so whatever the reason was for this specific episode to have a preview, it's not apparent to me. In addition, since I'm watching it via Netflix Streaming, I'm not sure if these previews were so sporadic when the show aired, or maybe they were present at the end of each episode when they originally aired, and then most of them got removed as part of the editing for the Netflix version.
Why do some Supernatural episodes end with previews, and others don't? Is there something special about these specific episodes that isn't immediately apparent?