Damaged (yellow) sectors in a ScanDisc Read Test (not the ScanDisc C1/C2 - PI/PO Test) usually(*) means that the drive had to re-read a sector because the first attempt failed.
This means that the sector can sometimes be read, and it also means that the drive can sometimes read the sector on the first attempt, which will show as a green sector.
For this reason you can expect that (some) yellow sectors will move around, appear, or disappear between scans.
Bad (red) sectors are much more likely to stay in the same place, since they indicate that the drive was unable to read the sector after multiple attempts.
(*) For some drives and when reading CD media I believe it can also mean that a C2 error was flagged.