Is it possible for discs to lose information without visible signs such as disc rot spots?
From my personal experience, all cheap/fake CD-R and DVD-R I’ve lost were without any visible signs. They wouldn’t be recognized by the drive or not all the data could be extracted. When scanned (if it was possible) they showed enormous number of PIE and PIF errors.
So far I have seen only two discs that had visible signs of failing - one DVD-R from Optodisc (12 years old from 8X era) that has dye discoloration in form of circles at the outer edge and one CD-R from TY (Verbatim Pastel branded) that has few fingerprint like pattern on the dye (I suspect that someone touched the substrate in the factory before the dye was spread).
I still haven’t noticed any problems with my factory pressed discs so I can’t comment on that subject.
Were your fake discs damaged from the beginning or did they actually degrade over time?.
They degraded over time but it wasn’t sudden or without warning. First signs usually are slow transfer speeds or sudden slowdowns when accessing data. After a while drive won’t recognize the disc on first insertion and it will take multiple ejections so the drive can achieve focus.
This was in the early 2000s when I was using CD (and later DVD) for short term storage and I was able to see this change of behavior in relatively short period of time and no data was lost.
Today, when optical media is used for midterm/longterm storage and is not accessed frequently, the only way of tracking degradation problems is doing quality scanning every year - visual signs are not the right way to check for degradation problems.
I still have one of those CDs - I keep it because I’ve never seen other disc from this manufacturer.
It is shown as empty but I can actually see where data was recorded - no visual defects at all.
I never experienced any long term data losses without visual signs. One CD-R burned in 2012 worked in 2014 for 2 times of reading after unused for 2 years. Then, all working drives suddenly failed to recognise it.
The first 4 seconds of data failed.