Interesting. Unless I’m not reading it right, it appears that some of the larger ships, Oasis included, will provide access before embarking. See wording below:
Lights, camera, action!
We're putting the finishing touches on our entertainment lineup, so if you're sailing on a ship that accepts reservations before you board*, check back closer to your sail date to guarantee your seat at our can't-miss shows.
*Allure of the Seas, Anthem of the Seas, Harmony of the Seas, Navigator of the Seas, Oasis of the Seas, Odyssey of the Seas, Ovation of the Seas, Symphony of the Seas.