Hi
I wonder if I could inject a new thread of thought into your research. In addition to the 2 John Westcott’s you have identified, I cannot see why you have discounted a further John Westcott who was baptised in Bishops Lydeard on 11th August 1845 to parents of William and Mary.
In 1851, he is living with his parents in Mill Lane, Bishops Lydeard with the head of the household being his paternal grandfather Joel Westcott. Joel was a former military man and a Chelsea pensioner.
I cannot link this John to the one who became a policeman in and around Frome a few decades later. As you say, these Westcott’s never stated their correct ages in the censuses. I notice that policeman John had a wife named Mary who in later censuses stated that she came from Langford Budville. This village has a number of families with the surname Crowcombe and I located a marriage between a Mary Crowcombe to a John Westcott in 1866 (Wellington 5c 531). If this is the correct marriage a copy of the marriage certificate would give John’s father’s name and maybe you will be able to tie this to James or Isaac or William who had their children baptised in Bishops Lydeard. Just a thought.
I have a particular interest in Bishops Lydeard as I was baptised in the same font as you potential ancestors and grew up there in the 1950’s. Also, a lady in New Mexico, USA who was a Westcott descendent from Bishops Lydeard sought my help last year. Her Westcott’s were not related to yours
Peewee