Well, it's technically anything about Batman's past that they want to reveal to us. If they wanted to tell something from Year One in a new issue, they could, but they've been trying to follow a linear pattern as such. Now, they are in about Year 6 after Barbara Gordon was cripled. Some other major landmarks they've already covered:
Issue 1 thru 5 -- Bruce Wayne becomes Batman
Issue 11 thru 15 -- Batman first confronting Hugo Strange and Catwoman
Issue 50 -- first confrontation with Joker
Issue 100 -- Dick Grayson becomes Robin
Naturally, they've taken a few issues off for present day stories like the Knight trilogy and the NML as well.
"No man can live on crimefighting alone"
- Adam West