I was curious and wanted to check the quality of my oldest media.
While testing I realised that for none of the media which were burnt before 1998 I was able to do an advanced scan (eg CD Bler with ODC)
Even for CDs in pretty good shape like http://club.myce.com/f33/scans-aging-older-cd-media-183176/index11.html#post2669986 it stopped after some second scanning.
What is the reason for it? Is this a general problem (different dye), does it depend on the reader or is it only a coincidence?