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Wee Hugh, I know your post is over three years old, but I just stumbled across it while googling the Sandy's family.  I am going through Parish registers for Miserden and the name Bayntun Sundys/Sandys comes up a lot.  I found a burial entry for a Sarah Harriet, aged 14.  She apparently died in Montreal, France (yes, it's a place in the Occitanie area of southern France) on 6 June 1832 and on 3 November 1832 was "buried in the family vault".  Maybe this might explain why there are no headstones in the cemetery?
Also there is an entry for Dame Mary Ann Turner Sandys, buried 18 Cambridge St, (I can't read the word, but it starts with P) and then looks like London S.W., 16 January 1879.
There are quite a few members of this family in the Parish register, including Sir Edwin Winston, buried of Winstone, buried 30 Dec 1838, and the link is here.  I realise you might have seen his burial, but thought all the other entries and reference to the vault might interest you.
https://www.ancestry.com.au/imageviewer/collections/5158/images/41511_633870_3975-00013?treeid=116740530&personid=102263396773&hintid=1032729959879&usePUB=true&_phsrc=sSk33&_phstart=default&usePUBJs=true&_ga=2.120344462.76233164.1617282424-1822737456.1613624189&pId=2386738