Error Correction during CD replay // Super Black Hole from Herbie's Audio Lab

Cros-Interleaved Reed-Solomon Code (CIRC) allows to recover data from up to about 4mm scratches along the track. Between 4-8mm data is interpolated while scratches longer than 8mm cause dropouts - at least for the most of CDPs working in real time (being not able to read sector multiple times). Ripping programs can go over sector multiple times until they obtain proper checksum. I had MAX (OSX) set to "Do not allow to skip" making program going forever with unreadable CD. I had few CDs that I was able to recover that way after couple of hours of ripping. Now I use XLD set to "Max Retry = 200".

I had CDP refusing to play because of dirty lens, then because it needed a little bit of grease to finally stop reading because of worn felt on the magnetic ring that supposed to hold CD down, allowing it to wobble. I had some original CDs with defect - visible wave in internal foil, as well as few CDRs with the same problem. The best CDRs I’ve ever used were Taiyo Yuden. Now I only use HD (server) with a couple of backups.

@kijanki Thank you for responding!! These last few years I got myself a hobby of reviving 1st generation Discmans. Have seen "all of the above" :-(

A few days ago I finally cracked and send an email to Steve Huntley, the designer of my Wadia (he is now with Resolution Audio). His response is below (posted without his permission, of course):
"There is a large variability in CD manufacturing and if the disc is not perfectly circular, or the center hole is off, or the pits are not equally spaced to the center hole its much harder for the player (laser and servo circuitry) to read it. So the lathe (Audio Desk Systeme CD Lathe) is exactly the right solution. Nothing specifically wrong with the Wadia...just picky about the discs it plays. Unfortunately discs themselves are not held to tight standards of manufacture."
"Of course a discman is designed to play anything and while the unit is jumping around all over the place....not exactly the design criteria of a Wadia mechanism. Also units (low cost players) have huge amounts of error correction going on so they can play CD's with peanut butter and jelly on them, kids finger prints, etc! That error correction does not help the sound....the less error correction the better. So again just a totally different design criteria."

What you and SH said confirms my suspicion that when I adjust Focus/Tracking gain, at low settings it skips easily but sounds better. Maybe unrelated, being spoiled by Wadia and Naim CDS3 it is difficult for me to judge the nuances of Discman's sound. 
@kijanki I bought all the books I could find on CD players maintenance and repair, most of them have a few pages on how pits are transformed into sound. If there is anything you can suggest on the theory of different DACs and error-correction, please let me know.

I will try to find something.  For now read this:
https://en.wikipedia.org/wiki/Compact_disc

I use Walkman CD players and Walkman cassette players. One thing that Walkman CD player has in common with full size CD players is vulnerability to background scattered light from the CD laser. The background scattered light is a combination of visible red light circa 650-700 nm and invisible near infrared light circa 700-800 nm. The background light is presumed by the rather dumb photodetector to be real signal. The green pen and other counter measures can be employed to amileorate this ubiquitous problem.