It seems as though when I use a config similar to the following I get no IPv6 servers in my pool selections.
pool us.pool.ntp.org iburst
pool north-america.pool.ntp.org iburst
pool pool.ntp.org iburst
only when I add a number prefix (as below) to the entries do I get IPv6 servers in my candidate list.
pool 2.us.pool.ntp.org iburst
pool 2.north-america.pool.ntp.org iburst
pool 2.pool.ntp.org iburst
Do I just not understand what should be configured?
That’s correct, for now it’s only 2.x.pool.ntp.org for example that have AAAA records for ipv6.
You can see more information in this thread: Intention to enable IPv6 by default in 2017
Also see http://www.pool.ntp.org/en/use.html and http://www.pool.ntp.org/zone/us which state the DNS entries that should be used. These include 2.*.pool.ntp.org.