there's also the dig shortcut to see the authorative ns in a oneliner
`dig -t soa` - usually I pair this with a quiet .digrc with +noall +answer to have a more terse experience
The MNAME field of the SOA record isn't actually used in DNS resolution so it could contain useless garbage. Recurring from the root as described by the blog post is the only correct way to determine a domain's authoritative servers.
thanks for clarifying that I cannot rely on the record