Board Thread:Wiki Discussions/@comment-25358381-20140918020735/@comment-26302001-20140918235342

for example, 01/01/42–12/31/42 bNB, means 42 years before Naruto's Birth.

01/01/1–12/31/1 aNB, means 1 year after Naruto's Birth.

Any other questions, you'd have to ask Seel he knows that timeline best.