Toronto. In the early days of photographic lens design there was no established standard for the data recorded on the lens. Early lenses usually had the patent number and/or date shown, but what else was needed? The coverage of the sensitive media depended on the choice of f/stop. The smaller the aperture opening, the greater the coverage.
Who made the lens was also deemed important. And its name, of course, but focal length, widest aperture, or angle of view were not considered important.
Consider the lens show here above (click image for a larger view). Made by Bausch & Lomb (in Rochester NY); licensed design by Zeiss; name of lens is PROTAR; series V (you have to look up the series in a catalogue or text book to know this lens is a wide-angle lens with a maximum aperture of f/18); Pat. Jan 13 ’91 (patented in January 13, 1891, likely in Germany); No 1648682 (serial number) 6 1/2 X 8 1/2 (coverage in inches at widest opening, full plate, larger cameras cannot use the widest aperture. A catalogue or text book will show the maximum usable aperture for larger plates).
On the body of the lens is an index and marks to show smaller aperture settings (if you have young eyes…), and the clearly marked word BACK so the photographer doesn’t mount the lens backwards and then complain about its quality.
The Protar series V wide-angle lenses were sold into the 1930s. They were originally called Anastigmat lenses, but Zeiss lost the court challenge on the name. The other Anastigmat/Protar series fell by the way side much earlier as better glass and better designs made the lenses redundant.