Hi there,
greetings from Germany.
These Abbreviations mean , if I do remember well: DC --> Digital compatible (APS-C) and DG --> Digital Grade (FF)
Please find a short list for Sigma lens explanantions here:
https://www.pixolum.com/blog/fotografie/sigma-objektiv-abkuerzungen
It is in German though, but I think SIgma offers something similar on theri international website too.
I do have the 35mm/f 1.4 DG Art, unfortunately the last one made for Pentax mount. I would not miss it, although it is not WR, the only point not so positive.
I always used to have some Sigma lenses esp. the old 24-70 2,8 DG, The old 70-200mm F 2,8 DG , the 15mm DG.
i ADORE THE 15MM f 2,8 fish-eye , a really great thing (diagonal 180°) and the 8mm f 3,5 circular fish-eye. Both great for Panos.
So all is fine. The 18-35 is an Art and as such, it has an outstanding image quality. There are many pics of our Luxembourg based member fs999 - btw. only a few km away from Trier
- that show its great performance. However, the vignetting is more than visible and cannot be completely removed.
Hope this may help.
Best from Trier
Georg