Hi Mike,
Cancelling a stand-alone Line from PCP will cancel the line (and all dependents) in CUCM; After which, DN will not show up in route plan report / PCP inventory.
But, if you cancel a shared line (same DN shared among multiple devices / users), only that line gets cancelled. DN information will still be in CUCM (as the DN is still in use by other devices / users).
That may be the reason, why you see the DN in route plan report even though you cancel it from PCP. Request your confirmation.