From my comparative tests of CD quality scanning, I suspect that the BenQ drives report only E32 errors as C2.
Usually E22 errors should be included in C2 (some sources say that E12 should be included as well, but I don’t know of any drive that does this). E32 should be reported as CU, and may also be counted as C2 in some drives.
I don’t think Nero CD-DVD Speed has the ability to display CU separately from C2, however.
I’m not completely sure about the BenQ in this regard, but it does show significantly fewer C2 than my NEC 4551 and Plextor PX-712 when scanning the same disc with deliberate defects.
So there’s a chance that the BenQ CD scans don’t show E22 errors but only E32 errors, which usually is the same as uncorrectable for an Audio CD. For data CDs there is a third layer of error correction, so CU isn’t the end of the world - but you definitely don’t want so see any on a good burn!
I have been thinking about putting together a thread comparing different drives CD scanning capabilities, but laziness has won so far.
See my example above as to why using a LiteOn DVD burner for CD quality scanning is more or less useless.