Well, this is a pretty common sense thing--avoid the 1st year of a new model. It's a general rule that's good to follow with most cars, as it sometimes takes the first year and real owners to find out some true issues and quality problems and eliminate them.
As far as a 2000 Deville vs. a 2001, I'd say from what I've briefly seen and read that various computer glitches were resolved, along with some build quality issues and a few minor suspension hiccups. Mostly it's all electrical, but that goes with a lot of new cars loaded to the gills with electronic everything. Some 2000's were real lemons, but some were also probably very good. It's just that the number of lemons went down with each passing year. If you can find a nice 2000 for a good price that doesn't appear to have anything wrong with it and you can find out at least some history on the car, I'd go with it. You probably have the same chance of getting a bad 2001 or 2002, you just never know when it comes to used cars.
An exception is our 1993 Caddy Fleetwood Brougham and 1992 Buick Roadmaster Limited--both first year models. The Caddy is absolutely flawless, and so is the Buick, with the exception of a few engine component issues right now, mainly due to high miles. Then again, these cars are based pretty much on cars that came out in 1977 and never advanced all that much--certainly not to the level of a new Deville!