Welcome to WebmasterWorld Guest from 220.127.116.11
The page was ranking in the 40's in very competitive area, after the duplicate was "removed" it has all but disappeared.
I have the same situation you describe (same page, different dates), and that is indeed the difference.
The only thing strange thing about the page was two full stops at the end of the title [another experiment fails!].
Las VegasOctober 6-8, 2015