ChanginMan1,
Pre-1837, London is almost a pit of doom genealogywise. You are reliant purely on church records and sometimes the christening records don't even give the mother's name at all. Another thing to bear in mind is that a large proportion of Londoners came in from outside at some stage, generally because that was where a lot of the work was. So we don't know for certain that Thomas FIELD or Elizabeth UNKNOWN were even married in London, since marriages traditionally took place in the parish in which the bride was born and christened. The normal procedure to get around this was for the bride and groom to get a Licence to marry elsewhere.
Also I am not enirely happy about that 1741 marriage in post #6. There are no children of that marriage christened at St Giles as far as I can tell. There are three chirldren of a Thomas & Elizabeth FIELD christened at St James Westminster, but one of those children was christened in 1740 - ten months before that marriage. I've looked at the Licences for London and there is nothing there. FIELD is not a rare surname, so looking elsewhere in England might provide several or many possibles with absolutely nothing to prove which, if any, is the correct one. Was the bride Irish, for example, as there is a marriage in Dublin which would fit? We simply can't be sure and we generally have to live with that.
The original registers for these London parishes are only available to inspect at the London Metropolitan Archives at 40 Northampton Row - they have a website - but are currently closed to the public I believe because of Covid19. But before scooting off to there (when they eventually open), I would recommend that you check and double check the information that you have. If you've relied on FamilySearch, let me start by saying that it is only a guide. It certainly does not contain all of the possible records because some dioceses refused to allow the Church of Latter Day Saints (Mormons) to photograph their records. This is particularly true of Herefordshire, Gloucestershire & Oxfordshire to name but a few.
We're always happy to discuss genealogy on this Forum and will help whenever he can. But we want to be reasonably certain that we are starting from a solid base and not going down a wrong path due to the original information being uncertain. Good luck with this and please don't take this as a knockback - I'm just trying to be helpful.
Maurice