You're right about the Ketheric comments and the Durge conversation- I remember I've used that line as a counter-argument to Astarion being that young before, but I also wasn't sure if he was doing elf humor or vampire humor. It at least sounds like elf humor though, and it is implying he was 100+ after death. I can't say for certain though. The disparity might come from different writers, since I'm very confident the durge scene we're talking about was written by Welch. But Rooney has also been seemingly inconsistent about Astarion's age. Perhaps it was truly meant as an easter egg for Newbon's age when he started? A mystery for the ages.

The thing about the date on the tombstone is that it was written quite plainly on the devnotes, so it wasn't the tombstone artists' mistake or something- but IDK if they just very quickly wrote it. The tombstone reflects everything written on the devnote except a small difference in the surname- The devnotes say Ancunín, while the tombstone reads Ancunin. This is because the alphabet they used doesn't account for accents like that.

I want to clarify that I'm not 100% sure the spawn siblings were playing cards- it's a silly detail but I dislike the idea of spreading misinfo or something :P I just remember they were like, hanging out at some table. If the tumblr blog hadn't deactivated I could confirm, but I suppose it's pretty trivial.

The current game does seem to point at him having the same role as the other spawn except he was the most hated, but EA seemed much more extreme. I also got the idea Astarion was out of all the spawn the only or one of the only ones that hunted people, but he didn't talk about his siblings much so idk, I just found it weird he specified his role as a spawn back then.
There are things I prefer about full release and things I prefer about how I imagined the EA version would play out (which I of course can't know because I haven't seen what they were planning, I'm just trying to solve the puzzle here). I think the father/son abuse angle is better and more narratively cohesive, and that the siblings also being tortured is better, because it's silly to think they'd be content in those circumstances. However, I was very interested by the possibility of Cazador thinking he was doing a twisted version of justice by punishing Astarion- a whole "abuser becomes victim" kind of plot for Astarion. It would have made a lot of people heavily dislike Astarion, though. I also think Astarion's arc could've been more complete if his past evils had been addressed, like the OG version seemed to plan on doing. I have more complex thoughts on what I liked about the whole thing and how I imagined it'd play out, but I don't feel super coherent or articulate right now.