Yes I'd noticed the anachronisms too and the phrasing of many of the transcripts is very similar. It'd be interesting to have a handwriting expert compare them, to see if the letter forms are in keeping with the supposed time they were written - I'm not sure how many people in those days would have been able to write to that standard.
Is that a line of enquiry you could pursue GPS Hella? That really would add to the credibility if an expert felt they were written by different hands.
I find this all very interesting as an ancestor of mine was acquitted twice at Exeter - 9 years apart, once for larceny and and once for arson. We're not trying to give you a hard time honest! It's just us family history types love proof 
I have to admit, although I am doing most of the research for our team, I am still a newbie in doing it. There are still a lot of things I have to learn about where to find what etc., especially because I only moved to England two years ago and, as you might have noticed, English is not my native language.
It would be definitely interesting to see if, and if yes, in which way the hand writings differ from the persons own writing.
I actually asked the medium (also thinking about the lack of education earlier centuries) what hapenned, when the person "on the other end" never learned to write. She said, that she would aid them then with her abilities, but the hand writing would always differ because of the personality of the person.

Well, I am not a medium myself, so I guess I don't have to know and understand everything

I agree, that there are a lot of charlatans around in mediumship, but there are also some that really have the gift to either talk to spirits or see things that happened in the past.
If the anachronisms come from "translating" or because she made the whole thing up (what I don't think)... well, we might never know.
Please correct me, if I am wrong... didn't the name "dad" already exist in the 19th century? And the word jail was definitely in use then (thinking about an old newspaper article I read today).
I don't have any dates except for Jethro Talbut, so who knows when these people lived? (if they lived)
I will also have a deeper look into this forum, maybe I can find some more helpful links.
I found, that court and police records, especially the ones you can find on the internet, have gaps, people aren't mentioned and/or their names are being distorted by either lack of orthography or misunderstanding, often because the people that were send to prison couldn't write themselves.
The older the records, the worse it gets

Thank you for your thoughts and some interesting ideas,
GPS Hella