Sorry for the double post, but I was not sure where I would get the best response.
Since the 1991 version of the red book standard (and possibly earlier) there has been an allowance in the dimensional section of the disk for a “stacking ring” on the top and bottom side of the disk. On the “read out” side of the disk, the stacking ring allowance is .4mm in height, in a zone from 33mm in diameter to 39.5mm in diameter. On the “Label” side of the disk, the stacking ring allowance is .4mm in height in a zone from 33mm in diameter to 44mm in diameter.
This being said, it is easy for one to find an example of a read out side stacking ring. Many CDDA disks have them as well as MOST CD-Rs. The difficulty appears to be finding any disks that have a label side stacking ring.
Does anyone know of any CDDA, CD-R’s or CD-RW’s with a label side stacking ring. I would be particularly interested in a published, readily available CDDA disk that is known to have this feature as well as any brand of writeable CD media that has a top side ring. I have been through my meager collection of 129 CDDA disks and 40 random CD-Rs found none.