@sleve_mcdichael thanks. I mean maybe it's overkill but if I made a page detailing what systems are included in which themes have would there be much interest in that? Could just run an excel vba macro or something to read the folders.
Although it gets confusing as with the open nature of the themes I've found a version of showcase that retro arena used, they added in a few extra images to the theme to include Atomisware and Naomi. So I just added those images into the stock RetroPie version of showcase.