United Mileage Expiration

I flew last week on united and the miles posted to my account. I am just wondering why the expiration now says 9/30/14? I thought they expire every 18 months? This would be 16 months. My dates of travel were 3/4 - 3/10, not sure if it matters or not.

One last thing I have a bunch of miles that were brought over from CO after the merger, am I in danger of losing those miles sooner or all my miles will expire at the same time. I am just trying to get some clarification

Thanks