Sampi OgonekSlobnoxiouswhat entails a level 3 scan?
The scan level 2/3 distinction is from before the FSS existed. Originally, scanning an astronomical body (which had to be done by flying to within about 5000 times the body’s radius, IIRC, and waiting several seconds while having the body targeted in front of your ship) would get you a level 3 scan if you had a DSS on board, and level 2 otherwise. (Back then, the DSS did nothing else, although it could be engineered to complete the scan faster, or increase the scan range.)
The way things work now, I think, every asteroid cluster you discover gives you a level 2 scan, and every astronomical body (star, planet, moon) you discover gives you both a level 2 and a level 3 scan. There is no stat available for the number of bodies scanned with the (new) DSS. (There is, however, a stat for the number of efficiency target bonuses received.)
(EDIT: only scans sold to Universal Cartographics count; it has always been that way, AFAIR.)
https://edastro.com/exploration/