PwerBI EM vCore Pooling

Customer currently has three Power BI Premium EM2 licenses (6 v-cores total). In their admin portal, those back two capacities: one 4 v-core and one 2 v-core. It appears the v-cores are pooled across the licenses and allocated freely, rather than each license being tied to its own capacity.

They want to be sure this holds if their license quantity changes. Specifically:

1. Is v-core pooling across EM licenses by design, and is it documented anywhere?
2. If they add or remove an EM2 license, does the pool adjust automatically, or do capacities need to be deleted and recreated?
3. If they drop from 3 to 2 licenses (4 v-cores), what happens to the existing 4 + 2 allocation?
4. With Microsoft consolidating purchase options and retiring per-capacity Premium SKUs, does anything change for EM at renewal or on a quantity change?
   
   Can they still pool vCores across the licenses and allocate freely or has it changed to where each license is tied to it's own capacity?