“Pressed discs don’t use dyes…”
Correct. The information is physically molded onto the polycarbonate that the disc is made of.
On the top of the disc, where the information is molded, a layer of aluminum is applied through vapor deposition and then sealed with a thin layer of plastic lacquer, spin coated over the top surface and then cured by UV light. This lacquer layer is very thin; thinner than a stand of human hair. Scratching the lacquer can cause permanent damage to the disc. On top of that, aluminum tends to be reactive and will interact with oxygen and other compounds; scratching and pitting of the lacquer can expose the aluminum to the outside. The lacquer can break down due to a flaw in manufacturing, but can also break down due to poor handling and storage. For instance, if you have a habit of laying a disc label-side down against a flat surface, that’s one way to potentially damage the lacquer seal; fine grains, such as from dust, can scratch and penetrate the lacquer whenever the disc is laid label side down. I can’t overemphasize the importance of always putting a CD back into a proper storage case when not in use, since a proper case helps to ensure the disc is protected, including the lacquer. Anything that can make physical contact with the potential of abrasion against the lacquer can cause problems, such as CD wallets, etc.
The problem with bronzing CDs was limited to discs produced by Philips DuPont Optical in Blackburn, England. PDO product from Germany and the USA didn’t have these problems that the English product did.
And, of course, there are several more CD replicators all over the world. Sega have used JVC Disc Manufacturing and Sony DADC for many of their Sega CD titles released in North America. Sega may also have used other replicators.