I have gone on to this site:
http://data.atoc.org/routeing-guide
How do I find if my ticket is valid via a particular station? The site is too confusing.
My route is Norwich to Stansted (not valid for London Terminals)
The railways don't like it when customers ask this question, because it's an indicator that you may be trying to extract extra value out of your ticket which is deemed to be something of a cardinal sin.
If you want a complete list of routes your ticket is valid on, you have to work with that site. But to do so to a reasonable degree, you need to have a detailed knowledge of railway geography, various documents of a very technical nature and access to a list of fares - extracting them from National Rail Enquiries for this purpose isn't designed to be easy so you might need to find another source.
According to the Conditions of Travel, staff are supposed to give you this information if you ask when buying the ticket. Give this a try and let us know how it goes! Alternatively someone on here might be happy to find out for you. Or follow Yorkie's advice if you have a specific route in mind - you might have to fight with the Journey Planners though as the options you can put in are limited.