Every disk has a serial number or stamper code around it’s inner hub. The serial number, while it can be faked, is rarely so, and that becomes a far more reliable way of telling the true nature of a disk. If there’s a mismatch between the media code and the hub code, you know it’s fake. There is no universal list of all serial codes and matching media codes, it simply takes time to learn how to identify real from fake media.
A lot of the key is using simple common sense. There is very little fake media sold at the retail level under major name brands in the United States or Canada. Most fake media in North America, as an example, is sold on places like eBay, where people try to pass off fake “Taiyo Yuden” brand media.
It’s also important to understand the difference between media that has simply borrowed a code for better compatibility, and a truly deceptive practice of trying to make you believe you are buying something you haven’t. Media that is made in China or Hong Kong, such as that sold under the Playo, Dynex, or NexxTech brand, is pretty much universally known to be borrowing codes, and there is no brand confusion, so that media isn’t really fake in the true sense of the word. Media codes are not something intended for end-users to understand or know about anyway, so the borrowing of codes is not an attempt at deception. Only when trying to sell a specific brand as something that it is not are you being deceitful, such as selling Verbatim brand media in the United States that isn’t made by one of Verbatim’s authorized manufacturers, or selling media that is supposed to be made by Taiyo Yuden in Japan, when it isn’t.
This is a simple and yet also very complex issue, and depends on what part of the world you are in, where you buy your media from, etc. Once you understand some basic rules though, it isn’t really anything you need to worry about.