Suites , mini suites, Caribbean, Baltic and Ligurian all have priority boarding. That can be a lot of people. So if too many have priority no one has priority.
Theoretically only Full Suites and Ligurian should have a 12.30pm boarding time , rest should have 1.00pm. However that is Theoretical and if staff let everyone with priority check-in when they arrive , and go to the front of the the priority queue , then the promise by P&O for full suites, which literally says "we will whisk you through Embarkation before the other guests" is meaningless.
I wait to see, but expect chaos.