I have finally managed to attempt developing this old film. There are good news and bad news.
The good news is that it worked: there are indeed usable photos from what appears to be 1940 or thereabout. I was hoping something would show, but I was also skeptical about it so it was really a great surprise!
The bad news is that there are only two exposures (although the roll was fully wound when I've found the camera). I am not sure if indeed it was not exposed, or I somehow ruined it.
The film (or better the two shots) is now drying, maybe I'll be able to share these two negatives.
I can't hide that I genuinely felt a chill down my spine when the film came out after washing and I could recognize a man and a woman in what looked like a snapshot from a vacation. The image looks a bit soft, even for "older" cameras. But there is surprisingly very little fog and the image is clearly visible. The second photo is less clear, I can see a field with a black car and sheep.
The rest of the film does not seem to have anything of value, it's like it's not been exposed at all. I may have made some mistake during loading or handling the film in red safelight (more on this later) but I would have expected to see at least something. Instead, I can only see some very faint bars of alternating densities.
Thank you Pentode for sharing the video with the trick to load the film on "one Paterson reel and a half", that's what I have done. I tried initially using my changing bag, but it was impossible to get the film on the reels that were not locked in position; I then moved to the darkroom, where I risked using the red-light. Even then, it was not easy at all and it took me a few attempts until I was able to finally load the whole of the film onto the spiral (I decided to load the end of the film first). Unfortunately, I had not considered the increased vertical height of this contraption (2 half reels on one side and one on the other), and when I closed the lid of the tank I pressed down a bit too much and ended up squashing the top reel downwards, which has caused creases on the film.
I had briefly considered tray development under safelight, but this would have been a new technique for me so I finally went for spiral and tank. I regret my decision a bit now that I have ended up making creases the films in many places.
I developed with HC-110 dil B for 10 minutes at 20 deg (averaging a few things I have found online), followed by water bath (I needed two to get clear water, it was slightly pinkish) and fixed for 4 minutes.
It was such a thrill, I wish I had another one to try once more.