Board Thread:Spoilers!/@comment-413929-20151029063935/@comment-26159109-20151103035920

The plan was 10 episodes in 5A and 12 episodes in 5B, and then abc added an extra episode to 5A making it 11. That move made 511 not be the 100th episode since A&E desperately want it to be the spring premiere so they said that 512 is 100th episode.