The last number in the model number is the year of introduction.
I just ran across this from Anandtech:
http://www.anandtech.com/showdoc.html?i=1855&p=15
"“What is the best 19" LCD?” — Another popular question. Unfortunately, again, they are pretty much all the same. The Dell 1900FP, Dell 1901FP, Planar PX191, Samsung 191T and Samsung 192T are all based on the same panel. There are about another 20 tier 2 and 3 manufacturers that carry monitors that look identical to the Samsung 191T as well. As far as we can tell, we have yet to find one that is not based on the same Samsung substrate as the other previously mentioned 5 panels. There is a slight difference in circuitry from one to the other, but do not think one display will perform differently than another. Again, it goes back to the issue of cost. The Dell 1900FP and 1901FPs seem to price rather aggressively, and they are probably your best bet."
Kind of sheds a new light on the issue! Can't seem to justfy spending $800 for the PX191 when the 191T can be had for $640! Also, I can get the PL190 for $600 which makes the mix more interesting!