I got the certificate for the above in the post yesterday. 4 September 1847. No real surprises except that I note that William and Mary each signed their names with an "X". Doesn't mean they couldn't read of course. Is it also possible they could write their names but were embarrassed to do it badly?
Reminds me of what I read about people from a Sussex agricultural labourer background often not being literate. I think there was a lot of unemployment/poverty in Sussex around that time too for the farm workers.