It has been almost 20 years, or at least, according to this article by Jeff Zimba. The Serbu Super Shorty
As a close friend of Mark Serbu I asked him at a Knob Creek Machine Gun Shoot to make me the shortest possible AOW, Any Other Weapon in BATF Jargon. The oldest emails I have about this are from August 1997, so it must have been the April shoot that year. The original prototype was built on a Maverick 88, had the spring loaded folding grip, but the action bars would bind, per Mark it required a little English. Mark promised to get me another with improvements, number 300 was a Mossberg 500 that functioned flawlessly. I mention the number 300, because he promised number 100 would be mine if he ever reached that many. As well I have a Remington 870 based one, and a Holster.
Now we have a myriad of copies out there. Mossberg has even started to sell the Compact Cruiser AOW. Then we have the Typhoon 12 with a 5-round box magazine.