VSO Inspector runs 2 types of scans.
Sector by Sector, and a FILE Scan.
Well, the one, the name says it all, starts from the 1st sector where there's data and reads each sector of the media until it reaches the end.
Now the file scan, it will open the file and read the whole file, just like if you would copy the file from the media to your hard drive, it would have to read each sector used by this file.
Good = Sector was read without any issues.
Problem = The sector could not be read (Bad burn, bad media) BUT after a few tries (6 tries max if I recall) it was finally able to read the sector and collect the proper data off the media.
Bad = Even after 6 tries max, Inspector could not read the sector/data meaning, if you try to read the data off the media, it may end up corrupted, or just plainly unreadable.
All my scan are 100% good (Sector & Files Scans).
I use 1st class media (Verbatim, Taiyo Yuden, Maxell made in Japan) and personally never burn above 4x.
Even if VSO Inspector gives you 100% Good, there are still an other quality test that can be done.
It's called a PiPo Scan, but not all drive supports it.
I have a NEC-3550a and it supports PiPo Scanning.
I use Nero CD Speed v22.214.171.124 to run the PiPo Scanning.