I should have said a little more. You can DV8 from DH on an ocean crossing and are guaranteed a PS BE seat IF.. one is available at the time you try to book it. (And remember, some "crossings" are not crossings.. i.e. NRT-SIN, and you are only guaranteed a coach seat... it's only a 7+ hour flight though.. )

But, back to the original example: I was scheduled to DH from NRT to JFK, and wanted to change to the NRT-ATL flight. Since you cannot change an end of rotation DH until after you sign in, I tried to do so, and the ATL flight had no seats available for PS in BE, but there were some in coach. Needless to say, I stayed on my originally scheduled flight until I git rerouted