Delegation can happen at a dot, but does have to happen at each dot. The current referral sequence is:

root-servers.net -> cctld.us -> localitymanagement.us -> miami.fl.us

And it ends there with an NXDOMAIN. Unsurprisingly, a list archived in 2009[1] is no longer accurate. If I'm reading this Internet Monthly Report[2] correctly, that domain came into existence in October 1998.

[1]: https://web.archive.org/web/20090909141302/http://neustar.us...

[2]: https://www.iana.org/archive/internet-monthly-reports/1998/i...