Boards can be created by anyone in JIRA. In the case where the project associated to that board is deleted, then the board filter would have no shares. Thus, only the owner of that board can view it. What happens when the users delete the project is that the filter will be removed from the sharepermissions table, thus the filter will be marked as No Shares. However, the filter is still listed in searchrequest table.

There is no feature to allow admin to have access to the private-filtered boards. Not even from REST API. Not being able to enumerate all boards using the REST-API prevents the admin from cleaning up the boards automatically while this can be a must in some companies environment.

This is a very crucial ability that the admin should have. Imagine when for performance reasons, the user needs to split their big instance with 1000 projects twice into 3 instances with 400 - 400 - 200 projects. They do this by cloning the instances and deleting the projects that do not belong to the new instance. However, when the boards are deleted, then the admin will not have the access to the boards anymore. Not even for cleaning up purposes.