top right corner of f1r, possible inscriptions

[oshfdk]

I'm not sure about the rest notes in the right top corner on f1r, but your approaches above quite clearly show the letters "AR" in that corner.

Note that so far I've tried to uncover this shape using only clearly visible elements on the scans, because otherwise there is risk of making the model overfit and creatively combine layers to show just what you want. The risk of this especially with the simple linear regression is extremely low, but I prefer to play it safe. I will certainly try directly using the points you provided as the training shape after I exhaust other possibilities.