It seems clear to me, just fine. Remember, the key date is *AFTER* Dec 31 of 2008. (I incorrectly stated 5 year look back previously. My oversight.)
So if *YOU* were the last occupant to vacate the property prior to the closing date on the sale, any period of time "AFTER" Dec 31 2008 *OR* from the date of purchase (whichever date is the soonest) that the property was *not* your *primary* residence is unqualified use. Your exclusion amount will be pro-rated acordingly.
Also understand the pro-ration is not based on the maximum exclusion allowed. It's based on a percentage of your "actual" gain. So if you have a gain of $100,000 with 30% time of unqualified use, then only $70K will be tax exempt and you will pay taxes on $30K.
