Just for the record...
-the first Schneider Symmar was an f/6.8 design, a Dagor-type lens. Made from before WWII into the early 1950s; coated ones have a red triangle on the beauty ring. Not that common.
-the next generation (that I think you're looking for) was introduced in the early 1950s and made until the early 1970s. Commonly called "convertible Symmar", they are easily identified by the secondary f/stop markings in green. You remove the front lens group, using only the rear group, to get the converted focal length. Earlier versions have chrome barrels, late production lenses are black.
-these were replaced c.1972 by the Symmar-S lenses, redesigned for better performance but lacking the convertible feature. Later versions are multicoated and marked as such.
-those were replaced c.1990 by the Apo-Symmar line, redesigned again for apo correction and with improved coatings.
-and lastly the ApoSymmar L lenses, introduced c.2000; apparently these used newer, environmentally friendly optical glass.
They are all fine lenses; I've used examples of all but the first and last series. Hope this helps!