Are some years of NAD 2200 better than others?

I've noticed some sell on Ebay for considerably more than others.
The basic watt per channel and noise cancellation improved through the years, peaking around 1987 to 89.
i think there was a X version and a non X version

i had the 2100 which had these two versions, only on the label and on the box but not imprinted in the unit