and if so, how do I find out how it differs from the current version (7.x)? Is there a way to get API documentation for old versions of the plugin?
We have a customer with what they claim might be a 5.x deployment of Google Earth Enterprise. We are attempting to develop a solution using the browser plugin, but dont have ready access to their deployment (it is on a secure network), and none of the personnel we have access to seem to know anything about the deployment other than it exists.
In general this type of product support question is better suited for the Google forums than StackOverflow.
That said, existing enterprise customers can contact file a support case, and request an older version (only current and last versions are officially supported).