A famous real example is with NASA, whose early space records have suffered from a Dark Age issue more than once. For over a decade, magnetic tapes from the 1976 Viking Mars landing were unprocessed. When later analyzed, the data was unreadable as it was in an unknown format and the original programmers had either died or left NASA. The images were eventually extracted following many months of puzzling through the data and examining how the recording machines functioned.
Another example is the BBC Domesday Project in which a survey of the nation was compiled 900 years after the Domesday Book was published. While the information in the Domesday Book is still accessible today, there were great fears that the discs of the Domesday Project would become unreadable as computers capable of reading the format had become rare and drives capable of accessing the discs even rarer. However, the system was emulated in 2002 using a system called DomesEm by the CAMiLEON project. This allows the information on the discs to be accessed on modern computers.
Encrypted data may also prove to be an issue, as the process needed to decode the data can increase complexity.Historically, encrypted data is quite rare, but even the very simple means available throughout history have provided many examples of documents that can only be read with great effort. For example, it took the capacity of a distributed computing project to break the mechanically generated code of a single brief World War II submarine tactical message.Modern encryption is being used in many more documents and media due to publishers wanting the promised protections of DRM.