I think a more correct place to look at would be the gTLD Applicant Guidebook[1][2], section "2.2.1.2.1 Reserved Names", which I guess should be updated to now include "INTERNAL".
Though that list apparently includes all reserved names, not only those reserved for non-public use.
[1]: https://newgtlds.icann.org/en/applicants/agb
[2]: https://newgtlds.icann.org/sites/default/files/guidebook-ful...