WordPress.com Stats plugin is not active anymore!
Last month I made few changes on my server and I had to migrate WordPress.com Stats to new domain(in my case new subdomain, but it doesn’t matter for the case) and I wanted to have old statistics to the new domain name.
I searched for solution and it was pretty simple.
1) You have to have new WordPress installation running on your new domain.
2) Then install and activate WordPress.com Stats plugin (not Jetpack!) (update: the WordPress Stats plugin is not available at this moment( and activate with your old API key (apikey.wordpress.com)
3) At this point you should see old statistics in your new installation. If so, you can upgrade to Jetpack and continue with using your site/blog.
If you have any problems with migration, please contact with WordPress.com Support and they will help you with migration process with minimum data losses. More info here