Pioneer drives cannot be counted on for scanning, as [B]Some Random Guy[/B] said above. They do not produce reliable results. [The whole story is a bit more complex than that, but in a nutshell they don’t produce reliable results].
You are better off doing a transfer rate test with the Pioneer to see if the disc can be read back. To scan DVDs, you’ll want to get a LiteOn, BenQ, or Samsung [or a genuine Plextor, not a rebadge]. To scan CDs, you’ll want a BenQ, Plextor, or Optiarc/NEC [LiteOn and Samsung don’t report all errors when scanning CDs]. There are some specific drives from each maker that don’t provide proper scanning for various reasons, though, so be aware of that.