Why are the numbers on the back of Ilford and Rollei 120 films so indistinct?

I an preparing an article on a particular sort of old film camera, one that has a red window in the back through which the frame number on the film backing can be read. These are not the cameras that space the film automatically when winding on, like the Rolleis, or Hasselblads or Bronicas  but the run-of-the mill folding cameras and box cameras from the likes of Zeiss, Agfa and Kodak.

I started by loading a 120 Ilford FP4+. Even taking into consideration my eyesight I had great difficulty in seeing the numbers through the red window. They seemed to be printed in a very pale grey, not black as they once were.

On processing the film, I kept the backing and discovered that the numbers were indeed a light grey and what made matters worse that for 12 exposures, the row of numbers in the middle of the roll, were the most indistinct of all.

I then looked at the backing paper from a roll of Rollei infrared black and white film. It was identical to the Ilford one, suggesting some film manufacturers are buying backing papers from the same source.

The scan below shows the problem:

The red window dates, of course, to the time of orthochromatic film which was insensitive to red light. Any red light leaking round the backing paper to reach the film would have had no effect. Even when panchromatic film became cheaper and replaced orthochromatic in common use, the red window remained despite the fact that a deep green window would have provided greater protection; only a few cameras had a green window but at least one had a shutter to provide a choice of red or green.