Really old Thinbloods

(flairing this as v5 because that's my reference but it's more of a general discussion)

So I know that Thinbloods are described as relatively recent (ish) development, a sign of dark times that are upon us, and that before they were very rare and killed, unless they "upgraded" themselves via diablerie.

However, something I keep wondering about: there are only 13 nights between Caine and the first 14th gen, and I find it improbable that this path has never been fully walked through during the literal millennia of Kindred history. As for the killing, it's not like there is a red alert button going off in the nearest Elysium when a new Duskborn appears.

So purely as a mental exercise, I imagine sometimes a very isolated offshoot of a very isolated bloodline living in the middle of nowhere that can Embrace new Childer up to 140th generation if they so wish, let alone 14th, without anyone really knowing.

So - again, purely as a mental exercise in this yet another heatwave - how would you go about designing a Thinblood who is older than a century but didn't diablerize anyone? How would they change without constant fear of execution and being reminded how inferior they are? Would their vitae still undergo some transformation with age when it actually gets a chance to mature? Or maybe they swing more towards their human qualities and the blood literally thins with decades?

I want your wildest TB headcanon homebrew!