Another contributor thinks it may have come on the scene even earlier:
In the thread asking how many had walked out 1000 lb squats, the question of the introduction of the Monolft came up. I said '93-'94, W. Williams and Bob G said earlier. Everybody was right. Here is a simplified scenario. By early 1993 there was a prototype model, and it was used in several meets. Madden discussed using the machine with Rich Peters for a late '93 Hagerstown met, but Rich thought the machine dangerous, that the jack was badly located and the machine capable of tipping. Some of the Peters bashers won't like him getting credit, but the two men redesigned the machine, moving the jack to the side at Peters' suggestion. This design was tested at Hagerstown and used at the '94 NASA National - and became the production model the game came to know.
Paul take a look at page 8 P/L USA Mar 93. It shows a monolift being used in Nov 92. It think it goes back further than we realize