I've just bought a 'Schneider Xenar 7 1/8 inch F3.5' barrel lens and the thing I don't understand is why it has an unusual serial number. It does not have a normal numeric serial number (eg 11,000,232) but is "No SC-178". It's also only labelled "SCHNEIDER", not Jos Schneider or Schneider Kreuznach or similar. It doesn't appear to be coated (but I could be wrong), so may be pre war but appears to be in good condition (mostly anyway) and looks much more like any lens made form the 50's or so.

I don't know if it's some weird fake or just an uncommon special purpose Schneider lens, maybe from the war years. Any advice would be appreciated as I can't find any references anywhere to this type of serial number on a Schneider lens.

Some pics of the lens in question:

Engraving looks odd on the focal length:

The image below is typical of Schneider numbering even for very early lenses (this ones approx 1970-80, I haven't looked it up).