Whether upgrading from version 2.x or 3.0, the 4.1 license provides you with a rich set of features.
Birder's Diary is no longer split into a North American and World version. Instead you can purchase a basic or advanced user license and then individually purchase only the taxonomic lists that you are interested in. When you upgrade from version 2.x or 3.0 of Birder's Diary, you are licensed for all the tax lists currently existing in your 3.0 database
Additionally, when you upgrade from v2.x, I do the lengthy and complicated process of upgrading your data for you! I deliver your v2 data to you in a v4.0 database. All you have to do is install v4.1 in minutes from this web site, and upload your v2 database to me. See the instructions above.
You will likely want to update the taxonomic lists you use to the latest versions available. As those available in v3 and v2 are many, many years old. Many changes take place each year and this means that you could be missing dozens of species with these old taxonomic lists.