No idea, wouldn't make a difference to me anyway as taking my daughter. They weren't available immediately but the seats were coming and going as I was logged on.
I got 2 tickets Block 105 row 37 yesterday morning about 9:30 as I selected family tickets it automatically allocated 105
Quite possibly because I put both membership numbers in (daughter is 11) it allowed me to order in those blocks.
I have just put my membership number in to see what seats were being sold and I could only choose blocks 517 and 519. I will be really surprised if we had sold all other blocks already ..