Allow the site-admin role to assign users to be 'editors' of specific content

[mattsqd]

The assigned users would not need to be given the 'Editor' role which can create and edit all content, instead, the can have no roles and be assigned on a per node (not content type, an individual node) instance.

https://www.drupal.org/project/editorial_access_manager might be a fit for this.
Hopefully this will not require some craziness with the groups module.

[mattsqd]

Also https://www.drupal.org/project/acl might be helpful.