Side by Side - Aside from the engraved text, the lenses look pretty much the same
The mounting plate is slightly different. Note the serial number on the Ross branded lens has a smaller number than the unnamed one. This indicates that early lenses had maker's name on the lens, and later ones didn't.
Ref. No. 14A refers to photographic equipment. Both the Royal Air Force and the Canadian Air Force use the same convention.
The major difference I see, is that the Ross branded lens has aperture settings to f32, while the unname lens only goes to f11.
Well, there you have it. I am willing bet a dollar that the unnamed AM lens was made by Ross London, and the two lenses should be optically identical. I haven't shot any pictures with the Ross lens yet, but will do so as soon as I get it mounted on my camera.