This is great info - thank you !

Something I haven't been able to find an answer on is whether witness votes expire or have to be renewed, or if once cast they remain permanently in effect.

It occurs to me that users could cast votes, then stop using Hive, and the only way those votes could be reduced is if they power down their HP, leading to a situation where the earliest witnesses could be propped up by "zombie votes" from a time when Hive had more active users.