Can a Lost Encoding Format be Recovered by Analysis?

It's now a decade ago that I read in a newspaper article that data obtained on Mars by Viking spacecraft could not be read 25 years after the landing because the format was lost (The Asahi Shimbun, 20 January 2014). The case is also mentioned in a report on long-term data preservation by a Japanese think tank, CRDS (CRDS-FY2012-WR-07).
The source seems to be a news release of the University of Southern California (Spaceflight Now):

"The data were on magnetic tapes, and written in a format so old that the programmers who knew it had died," Miller said.
Eventually, NASA was able to recover the data from printouts, luckily preserved by Levin and Straat - and so, Miller was able to pore over the numbers.

After all, the issue is not about loss of a data encoding scheme but physical format of the magnetic tapes.

I got interested in this news because I was wondering whether "codebreaking" is possible for media data encoded on, say, DVD without knowing the format. (The compromise of the encryption system (Wikipedia) of DVD assumes knowledge of the format, and is thus another matter.) Considering the sheer number of pages of format documentation, I think it is near impossible. But of course, relying on secrecy of the scheme is not a good idea for cryptographic security. Security should rest on the key being kept secret (Kerchoff's principle).

By the way, the Viking data recovered in the 1990s was used to claim finding evidence of an organism on Mars (Miller's site, Levin's site). But the result is not established (Wikipedia).