Yes, the stem would have been manufactrured in March 1996. However, I'd still try to detrermine the age of the other components. You don't know how long the stem sat in the factory, The more dates, the better the confidence in the age. Pending more info, it curently looks like it's a 1996 or 1997 model. BTW, are they RX100 components?

Over the past couple of days I've gone though my late 1990s's Canadian market buyer's guides, including both 1996 and 1997. There are no Nishik included in either. That suggests the brand was in very limited distribution and/or the distributor did not want to pay to include the bicycles in the guides. Which is curious, given that Norco was the distributor in the early 1990's and the Norco brand bicycles are included in both guides. This suggests that Norco may have divested itself of Nishiki by the period in question. Norco distributed Nishiki typically have a small (designed by) Norco decal on them. Is there anything to this effect on your bicycle?