All phone numbers are recycled unless you happen to get one from a new area code that was created.
Providers have a pool that they can choose from for native numbers and if one is ported out to another provider it will be returned when the account is cancelled. I do not know what pool of numbers Public is pulling from and where they originated, but they could have been split amongst other providers over the years.
When I worked at Shaw, I believe our initial batch of native numbers came from Bell as we were piggy backing on their ILEC processes.
