So, an update:
Regarding the Alton Quaker Deborahs (of the Dawes, Simmons, and Waring varieties), I've busied myself looking through the Quaker records on Ancestry for any further mention of them. I've found two burials which potentially rules one out, and definitely rules out another (which I've noted in a post above):
- Deborah Waring, daughter of Samuel Waring of Alton, aged 27, bur. 1788 at Burnhill Fields, London
- Deborah Dawes, aged 66, bur. 1826, and recorded in the Peel's Court Monthly Meeting records
Deborah Dawes is noted as not being a member, though I don't know if this refers to being a Quaker, or merely a member of that particular meeting. It also doesn't note her marital status. What is making me rule her out as being 'my' Deborah, however, is that the Deborah Dawes b. 1759 had a sister, Mary, b. 1757, who married John Wansbrough in Alton in Nov 1788, with 'Debh. Dawes' witnessing the marriage as a relation. My Deborah had her son, Thomas, baptised in October of 1788. Furthermore, there are subsequent children born in Alton to John and Mary Wansbrough into the 1790s, with Deborah Dawes serving as 'witness' on the birth records. Presumably this is the Deborah b. 1759, as I can't find another Deborah Dawes in the Quaker records who would fit.
Which leaves us with Deborah Simmons. She had numerous siblings, and the generous details given in Quaker marriages (namely, the long list of relations who witness the marriage) led to me searching for their records. I can find several marriage records for these siblings in various Quaker meetings in London, the latest of which is the marriage of Isaac Simmons to Rebecca Crozier on the 9th February 1790. No 'Deborah Grover' is named as a relation and/or witness, but there is a 'Deborah Simmons' named instead as a relation. This potentially rules her out as being 'my' Deborah as well. I can't find anything more about this Deborah Simmons beyond 1790, however.
Long story short, I think the three Quaker births can possibly be ruled out.
I also contacted the lovely people at the Sussex Family History Group, who keep a Wills Index, to see if any Thomas Grovers or Deborah Grovers were to be found lurking anywhere. They responded incredibly quickly, and...no Thomases or Deborahs whatsoever!
Very odd. I'm running out of places to look (during lockdown, anyway).