Following up on my questions about Jesse and Harriet's marriage date, I did a search on the 'findmypast' website. It's a site I've discovered where you can access all sorts of documents which are useful for family tree research. You can often view the original document as well (for a fee).
I searched for Jesse Pullen and again came up with more than one marriage record. This time, the third one was missing, and I am more confident now that my original hunch was right about that record being a transcription error.
But there were still two - which is curious! And when I looked at the originals, I did find out some new information and realised some of my assumptions were wrong.
The first marriage date was 11 October and was in Chartham, Kent. The banns had been read on the three consecutive Sundays - 27 Sept / 4 Oct / 11 Oct. This was in line with the other information I had found. I was also right that Harriet Kingsnorth was most definitely NOT a Kingsworth on the record (it's interesting that this has been such a common error!). What was more interesting is that Harriet was listed as being the one from the parish of Chartham. I had assumed it was Jesse since my other record for Harriet was her birth record from Headcorn. I wonder why she was living in Chartham? Jesse, on the other hand, was listed as being from the parish of St John's Margate. That's also a surprise, since he was from Chilham, Kent (just down the road from Chartham).
The second marriage date was two weeks later on 28 October (no mention of banns, just a record of marriage and the signatures of both). It was at St John's Margate.
I did a bit of research into marriage banns in England at the time, and the rule was that you needed to have the banns read in both parishes if the parties came from different parishes (you only needed to live in a parish for three weeks to be 'of this parish', so sometimes the groom would live with friends for three weeks to avoid that). It seems that in this case Jesse stayed living in Margate (I'm think he probably worked there) and they did in fact get married in Margate, but that the banns needed to be read at Chartham in advance.
I would still love to know why she was in Chartham - I'll keep digging!