I am also wondering this due to the range of Souchong prices I've seen. I've heard that some vendors spray on the flavor, which could be a cause for concern. Regarding freshness, since the flavor of this specific tea is smoked in, I imagine it stays fresher longer than the standard green if well stored, though I could be wrong.
Also, I have had a difficult time finding a Souchong with the underlying longan/dry fruity flavor I've gathered they are supposed to have in addition to the smoked pine--not that it is absolutely necessary because I like the smoked, earthy flavor of the one I have been ordering from Seven Cups, which is not at all expensive and seems fresh to me.
Here is the link in case you are interested: http://www.sevencups.com/tea_shop/Lapsa ... -2012.html
And here is a link to a more expensive one: http://www.jingteashop.com/pd-jing-tea- ... uchong.cfm