HELP!!

I am a little confused by this post.

"I applied for my sister's immigration to US 10 years ago, her priority date is Feb 2010. I looked at Visa bulletin, it's Jan 2010 now."

Why my brother's information is totally different: I applied for my brother's immigration to US 9 years ago(2001), but his priority date is June 21, 2001. I looked at Visa bulletin, it's 15JAN00 now.

Did I look at wrong information? What was wrong here?