I'm a boat
AFAIK the only supplemental product released for 1st edition Ars Magica, aside from the convention-only Bats of Mercille.The broken covenant of Calebais is an ARS Magica game.
It's also the last AM review until #170, which looks at a number of the later Lion Rampant products for the 2nd edition. (The line got a relatively low amount of coverage in Dragon's reviews, despite the large number of books released for it. Not entirely surprising, I suppose, as it was aimed at a different market than the typical Dragon subscriber.)