Note that extensions and queues can have a different set defined such that:
If the extensions have the default selected (under their voicemail tab) then they will hear the default set for their operations regardless of which System Prompt set you have selected, and therefore they will have updates applied to them if published by 3CX
If you create a custom set and select it, then any new extensions created will follow it, and also any incoming calls will hear the custom set (since its the System wide one)