You can be registered for multiple events at the same time, but you can only be active in one.
Active means playing games of Magic the Gathering (byes do not count towards being active). Checking in to build your Sealed Pool also counts as 'active' for registration purposes.
If you become active in two events, you will have to choose and drop from one of them.
If you drop before being active, or no-show an event, you will not receive PWP.