Yes, but they weren’t oversights, but rare artifacts of a transitional era
Since E. Leitz Wetzlar was almost fanatically fastidious about engraving serial numbers on its cameras and lenses (even accessories!) and in keeping meticulous records that have proven to be of immense value to historians and collectors it’s kind of astonishing that there are a fair number of vintage Elmar lenses floating around that are utterly devoid of serial numbers in the usual places. The most common ones are nickel finished 50mm f/3.5 collapsible Elmars with no tiny numerals on the front of the black aperture setting ring. There are also a number of early black finished 90mm f/4 Elmars (affectionately known as Fat Elmars), and a much smaller number of exquisitely petite early 35mm f/3.5 Elmars, neither of which have the usual serial numbers engraved on their front lens I.D rings.
How did it happen? Well, the period between 1930-1932 was a an intensely active time of rapid transition at Leitz. The foundational fixed-lens Leica I model A was being replaced by the new Leica C which accepted interchangeable non-standardized screw-mount lenses, each of which had to be individually matched to a specific body and weren’t rangefinder coupled. Shortly afterward the standardized mount version of the Leica C arrived, which utilized standardized screw-mound (LTM) lenses. And finally, in 1932 Leitz unveiled landmark Leica II or D with standardized interchangeable lenses that were coupled to the camera’s ingenious built-in rangefinder. Understandably, many Leica I owners wanted to upgrade their old cameras to Leica II specs, and E, Leitz Wetzlar was only too happy to oblige, not only to serve and maintain their loyal customer base but also to expand the market for its new line of interchangeable Leica lenses!
If a model A was returned to Leitz for an upgrade the original 50mm lens unit (which had no separate serial number) was removed and remounted, and if it was destined for a Leica D, it was remounted in a standardized rangefinder coupled focusing mount. The nickel 50mm Elmar (no external number) shown here may be such a lens, removed from a Leica A and upgraded. The fact that the lens is marked in mm rather than cm is a practice that extended well into late 1931. However, the 9cm f/4 “Fat Elmar” in the accompanying photo, which is marked in cm probably dates circa early 1932. Note: Some of the very earliest 9cm Elmars were not rangefinder coupled and the lowest that have external numbers, which date from very early 1932, begin at about at about serial number 94XXX.