All the testing of these things is somewhat artificial. And it sometimes doesn't catch the external effects. Some CD-rot came from materials used in the packing, not from the CD. It's always worth burning a CD at a bit less than the maximum speed of either the writer or the CD. It makes the dots a bit sharper, because of the time needed for the laser to switch on and off. In the early days, Kodak made a highly-regarded CD-R, and these Delkin CD-R's sound quite similar.