Commercials for the actual seasons and show. When you bought stuff from amazon they would ship cardboard boxes with ads for the boys printed on them instead of their regular packaging.

In regards to late night interviews and YouTube shows just doing quick searches you can find a handful of them. Even with characters from season 1 who were barely in the show. For magazines EW has them on the cover for season 3 which akes sense that they would do later seasons because the property wasn't big enough for them to preemptively feature them before release.