How do I find which closed or inactive client a Bill Layout is assigned to so I can delete the layout?

I want to delete old Bill Layouts I no longer use. I am unable to delete them because they show they are assigned to a client. However, they are not assigned to any current open clients and therefore must be assigned to "closed" or "inactive" clients. How do I find which closed or inactive client they are assigned to? All assignments under Bills, Bill and Statement Layout List only show open clients.