And to complete the post, some weak sectors (like the old 14B9 pattern) can be successfully be written onto a CD-RW, cause as said before, these lands and pits are quite different to a burned CD. The organical dye will perfect match that sector, and if the drive cannot write it at all ( as shown in SD 2.40 to 2.51 for some plextor) the "incomplete" sector will appear as is, so failure.
In a CD-RW, the read sector is not as easy to read as onto a CD-R, so some correction must be done. Then, will always succeed (excepting some toshiba: SD-R1402) and copy will work.
To conclude, on CD-RW some sector are not perfectly read, and were corrected to good one by the reader. On CD-R that sector are not perfectly written and are detected as is, with no correction needed.
Some weak patterns verifies that, and makes copies not to work.
And that is.