Thanks Bookbox. Combined or separate registers didn't occur to me. Might be worth me going through those churches that the St Sepulchre Vicar may have combined with as I have someone who I know was born in the parish but doesn't appear anywhere in the St Sepulchre registers.
I found an article on The Great Fire from 2016 in Church Times you might find interesting:-
During the rebuilding process, several parish churches erected temporary structures which they called “tabernacles”. All Hallows the More established the first of these in August 1669, financed in part by the sale of the church’s melted lead and bell metal. The term’s Nonconformist associations developed only in the 18th century.
https://www.churchtimes.co.uk/articles/2016/2-september/features/features/alight-by-the-hand-of-godShame they didn't say which churches took this option!