According to project-haystack.org the values for the kind tag are an enumeration of strings that start with uppercase characters then continues with camel case such as "DateTime". Acronyms have all uppercase characters such as "NA".
https://project-haystack.org/doc/lib-ph/kind
In the Kind enumeration in haystackc-core, all values are lowercase. I ran into this using the Kind enumeration to set the kind tag on a point. I observed the differences using a skyspark database, then consulted the documentation.