[ChrisArchitect]

Not sure which version they're referring to here but from Xiph updates...

> The latest draft of the FLAC specification by the CELLAR working group of the IETF. This more formal specification improves on the format description you can find further down this page. It provides a better explanation of concepts like wasted bits, the implications on subframe bit-depth of using stereo decorrelation, explanantion of the actual symbols used in rice coding, inclusion of various decoding, etc

So it's just likely a long process on a path for formal definition, that was only started relatively recently in the format's history.

See also:

https://datatracker.ietf.org/doc/rfc9639/

[ChrisArchitect]

Further, from scanning some forum/list discussions from a few years ago, the thinking or motivation seems to be benefits for implementers having docs to make building a FLAC decoder easier. Which indirectly benefits users with good implementations. And then for long term storage/archival having the standard defined in an open/official document helps ensure it won't fade into oblivion. Or succumb to implementations that are incompatible with future hardware etc. Protected by the IETF as it were. I suppose MP3 went thru similar steps many moons ago.

The CELLAR group's charter is like a broad vision rather than a specific internet format scope. https://datatracker.ietf.org/wg/cellar/about/