An unusual Genta’s UG?

Good morning,
Let me appeal to the knowledge of the forum to learn more about this manual UG with very nice diagonal line dial.
The outer case back bears the reference 28803 1 and at the bottom the case serial (1.8xxxxx).
The dial looks quite unusual with the Maison inscription at the bottom and a small notch, at the top crossing the 12-hour line.
People more experienced than me confirm its originality.
On the net I have seen only one other model with the same reference (but with different hands) called "Extra -Flat" and it even seems to have been conceived by Gérald Genta 😏.
Here is the site from which I extracted this info

https://www.timeline.watch/watch/1953-universal-geneve-extra-flat-ref-18815-1-33mm-gold-case/?cat=19

Since I am navigating in the dark, any opinion/info/advice is welcome .

Thank you very much,
Ilio

I'm afraid that you'll have to do better than "I would say its was designed by the genius Gerald Genta". It's an opinion, that is all and unfortunately these things have a way of becoming "facts" with time and repetition.