While exploring secp256k1, I came across what seems like the official definition at https://www.secg.org/, specifically in https://www.secg.org/sec2-v2.pdf. In terms of authorship, the document only contains references to the Standards for Efficient Cryptography group and Certicom (acquired by Blackberry). However, many resources I come across mention "NIST curves" in the context of secp256k1.
I've searched https://www.nist.gov/publications for definitions of the curve, although wasn't successful. The document's only mention of NIST is as a reference to "National Institute of Standards and Technology. Recommended Elliptic Curves for Federal Government Use, Jul. 1999", which doesn't seem to be available at NIST anymore, but can be found here and seems to contain different curve definitions.
So what's the relationship between NIST and secp256k1? Is NIST the author of secp256k1? What's the relationship between SEC and NIST? Why does the bitcoinbook say that NIST established secp256k1?
Bitcoin uses a specific elliptic curve and set of mathematical constants, as defined in a standard called +secp256k1+, established by the National Institute of Standards and Technology (NIST)
How does NIST fit into the story of secp256k1?