Yes, you’re correct. See http://www.sigmaphoto.com/lenses/lenses_chart.asp and scroll down to the bottom where it talks about DC lenses.

I suggest you look at www.slrgear.com they have extensive tests on many lenses, nikon as well as sigma.
Check out the chromatic abbrasion, vignetting and sharpness charts.

It’s the place I go to when considering new lens options.