Some of the month/day names in the culture data weren't right in Everett, so those have been fixed.  This post goes along with idea that you shouldn't trust culture data stability (http://blogs.msdn.com/shawnste/archive/2005/04/05/405694.aspx).

ar-MA, nn-NO, kn-IN & div-MV are all locales that change their month &/or day names in Whidbey.  This changes parsing behavior for these cultures.  So if dates was formatted with one of these cultures in V1.0/V1.1 and then that data was read with Parse or ParseExact in V2.0, it may not be recognized and throw an exception.

When persisting data it is recommended that you use CultureInfo.InvariantCulture or a binary format or some other method that isn't subject to change.  CultureInfo.InvariantCulture is the only culture that won't change between versions and cannot be replaced by a custom culture.