If a person already existed in your main PCO People membership account, but had not been added to PCO Services for scheduling, Schedulers were unable to import them for scheduling. However, in many cases* they were able to create a completely new person.
We've updated it so that if a Scheduler can create a new person, they can also import a person from PCO People. Otherwise they were likely to create a duplicate person, causing confusion.
* This only applies if your PCO Services site settings have "Block Schedulers from Editing People" set to false.