@Tom...Ok, was just a thought...

Another thought.....This may be a bit off the wall, but....here it is...

The lasers used 5+ years ago to burn (and read) were not as advanced as those today....I believe the older ones used a "wider" beam because burns rates were much slower.
If this is now being read in a newer CD/DVD reader/burner....it may be having problems with the way it was originally burnt.

Like I say, just a wild guess...hopefully someone can jump in here and correct me if I'm out to lunch.

Regardless of how it  happened, it looks like you have lost those files.

Regarding commercial vs "home burn....yes, my understanding is that the commercial ones  are "pressed"....but I doubt that they will last forever as there are many factors that could lead to data degradation.....one being "oxidization" of the layer itself.   That can happen when the edges are not properly sealed and exposed to air/moisture.

A final thought....I would suggest that using RW discs for back-up would not be the best approach in any event.....writes and re-writes just increase your chances for problems.

In youth, we learn....with age, we understand.