In 1992 and 1993, two Japan-exclusive Dragon Ball Z specials, Dragon Ball Z: Movie Overview Special and Looking Back at it All: The Dragon Ball Z Year-End Show!, respectively, aired only once, and as such, have become very difficult to track down.
The former of the two (the Movie Overview Special, which aired in mid-1992) takes place shortly after the events of the 1992 film Dragon Ball Z: Super Android 13!, and features Goku and Gohan in tuxedos, discussing all of the Dragon Ball/Dragon Ball Z movies as of that point in time. The 45 minute special ends with Goku changing back into his regular get-up, while Gohan struggles to wrestle his tuxedo free, before personally advertising Dragon Ball Z: Super Android 13!, which was, at the time, playing in Japanese cinemas.
The latter, (the Looking Back at it All special, which aired on December 31, 1993) while similar to the previously mentioned special (at least, in terms of their irregular episode structure), is slightly different in that the characters (i.e. Goku, Gohan, Goten and Chi-Chi) are seen discussing various events from Dragon Ball Z that had taken place that year. The special ends with Goku telling his family about Pikkon and the Other World Tournament, with Gohan finally remarking that the adult division of said tournament was set to begin in 1994 (a more subtle in-show advertisement for the series).
While 13 minutes of footage from the Movie Overview Special have shown up on YouTube, the latter 3-minute video being of much higher quality than the 10-minute clip, the episode in its uncut entirety was seemingly unavailable until dycaite found it in full on a Polish DBZ forum in July 2014, alongside a cut-down version with the commercials missing. Similarly, 5 minutes of footage from the Looking Back at it All special have also been made available via YouTube, with the full episode, however, remaining elusive to fans.