Hi Brian
I have posted extensively my thoughts on here and to Malcolm Bull's site and you will see how much my Hartley family is moving around the country, and outside UK too, so I wouldn't rule anything out. There are quite a few possibilities given in my posts from which your line may spring.
I would look for information in the various archives, including but also beyond the registers, and don't forget newspapers. Halifax archives have a brilliant online index to the Halifax Guardian. The non conformism events may be a surprise but it is fact. Also another way forward would be to try sort out the various Davids in the 18th century.
If it was easy it would be boring!
Andrew