One odd "lost chapter" to a famous television show is what happened to the Britcom "Are You Being Served" between seasons 7 and 8 - as the actors wanted to work on other projects, two forgotten seasons were actually produced in this gap featuring Mr. Humphries (John Inman) being transferred to Grace Brothers' Australian branch, with 'new' characters who were just blatant recasts of the familiar characters.
While these two seasons are universally ignored as part of the show's canon (never re-aired, the complete DVD set leaves them out, and they've never seen home video release), almost all of the episodes have emerged on the Internet in recent years, some time-coded, evidently pirated from a television archive.
Oddly, all have found their way online except *one* episode - "Mrs. Crawford, Senior Person," a rewrite of the more familiar AYBS episode "Mrs. Slocombe, Senior Person." While this episode does presumably still exist, it was the only episode from the two 'lost seasons' to not escape the archives.
AYBS: DU [as you called it] is basically a non-canon Australian export of the original series [produced by the now-CBS owned, Network 10] much in the same vein as the Are You Being Served film(s) and Are You Being Served Again It lasted for 2 seasons and 18 episodes for the 1980-1981 season
And furthermore, It's never aired outside of Australia nor shown in reruns in Australia since it's original run
Yeah, when episodes pop up online (and they all have, except for this one), they're usually labeled "AYBS? Down Under" or "AYBS? In Australia" to make them distinctive, since many of them share titles with the UK version.