I failed to notice that when I reviewed the update, but I think "in parallel" is wrong in step 11 of the getAvailability algorithm which instructs the user agent to "Run the algorithm to monitor the list of available presentation displays in parallel".

In practice, if the algorithm is run in parallel, that means the first time an app calls getAvailability, it will always end up with a PresentationAvailability object whose value is false (set by step 9.1 since the list of available presentation displays is empty to start with). Is that the intent? I would rather expect the value to convey the outcome of running the monitoring algorithm.