The Retinas were made in Germany, and like other German cameras had available to them a wide range of accessories, including filter, lens shades, close-up lenses, viewfinders and more.

The one thing that the German camera makers did was standardize many of their accessories, so that they could be used across a series of cameras, instead of requiring the user to buy a new filter or lens shade for every lens or camera.

I'll dig out my Retina IIS and see if can share filters from the later folding Retinas (b/B, c/C). A lens hood for the folding Retinas is a bayonet, so it won't fit the IIS and probably wouldn't fit the Automatic III.