One major problem being that data stored on obsolete formats often cannot be read any more. This website illustrates the problem, the CROOK operating system for a Polish minicomputer called the MERA-400 was sought. A copy of the OS had survived but it was on magnetic tape and there was no easy way to read the media.
Luckily with some ingenuity and hardcore geekdom a way was found to read the tapes. In the end they found multiple copies of CROOK, other old operating systems and some other thought-lost software which can now be read and saved for humanity.
|ICL tape drives at the National Museum of Computing|