You could be right that it should read 1789. The transliterated surnames of the fathers are possibly incorrect too. You can read what the editor had to say here. Old cursive Hebrew can be very difficult to decipher.
http://www.rootschat.com/links/04mj/ However, after reading a few pages of Todd Endelman's
The Jews of Georgian England 1714-1830 on google books, I think anything was possible!
Justin
