I'm doing some genealogy work right now on my family's old papers covering the time period from recent years back to the late 17th century. Handwriting styles changed a lot over the centuries and individuals can definitely be identified by their personal cursive style of writing and you can see their handwriting change as they aged.
Then you have the problem that some of these ancestors not only had terrible penmanship but also spelled multi-syllabic words phonetically since they likely were barely educated kids who spent more time when they were young working on the farm or ranch instead of attending school where they would've learned how to spell correctly.
I don't know whether your LLM can handle English words spelled phonetically written in cursive by an individual who had no consistency in forming letters in the words. It is clear after reading a lot of correspondence from this person that they ignored things that didn't seem important in the moment like dotting i's or crossing t's or forming tails on g's, p's, j's, or even beginning letters consistently since they switched between cursive and block letters within a sentence, maybe while they paused to clarify their thoughts. I don't know but it is fascinating to take a walk through life with someone you'll never meet and to discover that many of the things that seemed awesome to you as a kid were also awesome to them and that their life had so many challenges that our generations will never need to endure.
Some of my people have the most beautiful flowing cursive handwriting that looks like the cursive that I was taught in grade school. Others have the most beautiful flowing cursive with custom flourishes and adornments that make their handwriting instantly recognizable and easy to read once you understand their style.
I think there are plenty of edge cases where LLMs will take a drunkard's walk through the scribble and spit out gibberish.
I'm reminded of an old joke though.
Ronald Reagan woke up one snowy Washington, DC morning and took a look out of the window to admire the new-fallen snow. He enjoys the beautiful scene laid out before him until he sees tracks in the snow below his window and a message obviously written in piss that said - "Reagan sucks".
He dispatched the Secret Service to the site where samples were taken of the affected snow and photos of the tracks of two people were made.
After an investigation he receives a call from the Secret Service agent in charge who tells him he has some good news and some bad news for him.
The good news is that they know who pissed the message. It was George HW Bush, his Vice President. The bad news is that it was Nancy's handwriting.