For once I am probably the most knowledgeable person who can answer this question
I work for an online image library, and a good proportion of our material from photographers and agencies comes in the form of CD or DVD. Over the past 2 years we have uploaded more than 7TB of data from such medias... You can do the maths and figure out how many CDs we have come across
As I am in charge of hardware, I can safely say I have seen all of the problems you can get from badly labelled CDs. I even had to clean the mess from
exploding CDs a few times
Here are my observations:
* Round CD labels designed for CD are usually fine. However when I go back to some of the first CDs we uploaded, often the labels are peeling at the edge, or pulling the reflective surface too much thereby corrupting the data on the outside rim.
* Other kind of labels are a big no-no: we have all kind of problems with those; they put the cd off-balance; the glue is not designed for CD and over time
eat throuh the protective layer, but worst of all, some labels come unstuck in high speed drives, and when they take a bit of the protective layer with them you end up with an
explosive CD* Markers which are not designed for CD slowly eat through the protective layer and end up corrupting data or rendering the CD unreadable
* Markers which are too sharp risk scracthing the very thin protective layer with the same result as above
*
Markers designed for CD are fine. And that is the only safe way of labelling CDs. Furthermore, if the CD does not have an additional layer for writing (ie: manufacter printed), as soon as you start writing on the protective layer above the refelective layer you start increasing the error rate. In this case, if you really value your data only write in the
inner transparent ring.
And in any case:
CD do not last 100 years. Depending on the brand they start losing data from the moment they have been written.