Good evening Rob and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with this topic.
Can you please confirm that if transitioning from Events Calendar to Event Calendar Pro you current posted events remain intact and do not have to recreate?
Before any major change to a website, it is always good practice to make a backup of your database. Just for extra safety.
That being said, extending the Events Calendar by adding the Events Calendar Pro does not delete or impact any existing event.
All pre-existing events will remain intact.
Let me know how that goes.
Best regards,
Geoff B.