Billericay - London Terms: ANY PERMITTED - Validity to Fenchurch Street via Emerson P

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Lets say I held a Billericay to London Terminals (Any Permitted Route Ticket) SDS Single.

The National Rail website says that where a ticket is to London Terminals:

Tickets issued for travel to/from London usually show 'London Terminals' as the destination/origin rather than naming a specific station. This is because the ticket is valid to more than one London Terminal station provided it’s on any reasonable line of route.

Using the Bukitlawang shortest route engine, the shortest route to London Fenchurch Street is via Emerson Park. However, the National Rail Journey Planner will not allow this route to be returned (I am aware of the fact this does not necessarily mean that the ticket is not valid).

I am aware that with Travelcards, the shortest route is calculated by reference to whichever Boundary Zone 6 station you can normally travel through, and from my experience with the Rochford to Zones 1-6 ticket ANY PERMITTED ticket this includes using the shortest route where that route is not permitted by the routeing guide (the journey planners agree with me on that point).

So, my questions are as follows:
1) is the ticket from Billericay to London Terminals valid to Fenchurch Street via Upminster?
2) What are the rules when calculating which London Terminals your ticket is valid to (other than that you must reach them using National Rail services and not cross into stations that are exclusively in the London Thameslink group)?