I see the Audit Trail tab on most of the projects in our environment. But there are some projects that have been created that don't automatically have the Audit Trail tab across the top. How can I add this to both individual projects and across the board?
There are two Global access rights related to Audit Trail information. These are not specific to an object (i.e. project, resource, etc.), but global to all audit data for objects the user has access to.
These can be added to a Group and users who need access to audit trail information then added to that group (best practice) or they can be added to specific users.
Assuming that the access is set up properly, can you check the Page layout code of the projects for which Audit trail tab is not visible. Then Go to the respective Page and see whether the Audit Trail tab is Active or Inactive?