Can't speak to reliability. You might want to
consider the relative
size of the scanned PDF docs that are common versus the size of the mini
cds. The rectangular ones can be as small as 50 MB or less.
I have old CD-Rs as old as 1996 vintage. This is an old Gold + green TDK
CD-R. But do new CDs has the same reliability record???
This is an excellent question - how to preserve data, and a recurrent
one on this list :)