Leica R lenses: Focal length designation on barrel

When did Leica/Leitz start to print the focal legth designation on the side of the barrel? I tried the search funtion, Puts and all, but to no avail.

Do you mean the exact focal length, as opposed to the stated focal length. I haven’t examined my R lenses, but for rf lenses, Leitz always scratched the true focal length on the barrel below mount. For example f49.6 on 50mm lense. Of course, the true focal length varied from lense to lense. This info was for the convenience of technicians working on cameras And lenses.
Have no idea if other users of the Leica brand name continued this practice.

No I mean the large focal length number in that square font, am I wrong to believe that it only appeared on 2nd generation lenses (end1970s onwards)?

For example here, on the Summmicron, on the left side:

The earlier version did not have it:


I am obsessed by such details. Someone in Solms, Wetzlar or Canada City must have decided to change this, and made a note in some obscure technical handbook. No?

Update: I found someone saying: "The E55 lenses have the focal lengths marked in yellow on their barrel", so the older lenses with the smaller filter threads don't.