The article from Zwiftinsder about the race calendar cleanup says following:
„Converting Club Events to ZwiftPower Races
One reason Club organizers don’t like the idea of their races being “privatized” is that Club events don’t show up on ZwiftPower. But James mentioned in the Facebook thread that “Club events can be added to ZwiftPower,” and this is an intriguing proposition.“
Can someone tell me how this is working?
Thank you very much! 
If you’ve got race organiser privileges in ZP, it is as simple as adding the Race ID on a hidden ZP page. It’s easy to do, but you have to have organiser privileges in the first place.
One of the bigger issues with club events is the limited configuration options - for example you have to have powerups enabled and can’t choose which ones.
Great, thank you James!
We add all our Club races to ZwiftPower and don’t have special Zwift Power rights.
Just go to ZwiftPower - Login and enter the event ID that can be found from the shared link.