One trick not mentioned in the article is to repeat the ddrescue with the same CD in different drives; this almost entirely saved my unreadable CDs, as no single drive could read them entirely.

My biggest savior was a Pioneer BDR-AD07BK which managed to read some discs that other drives couldn't even get the TOC off!

I wrote a gnu-ddrescue wrapper back then to avoid accidentally resuming a read to the wrong iso (only ever tested on alpine): https://github.com/9001/usr-local-bin/blob/master/miso