Hello Mike,
Thank you for your reply.
Point taken about the routeing guide, though my badly-worded intention was to highlight that the routeing guide is comprehensive and allows to analyse each rail fare. The same goes for your very helpful Fares Guide in that it allows one to analyse the fare structure to make informed choices about how to plan journeys. For example, it makes it clear that if travelling from Chiswick House to the South Bank, it would be cheaper to use the Tube from Chiswick Park than National Rail from Chiswick. Furthermore, it allows to conclude that walking an extra 5 minutes to Turnham Green makes the journey cheaper still. I am trying to find a similar information source for analysing fares but with journeys from Reading. After reading your post I might try contacting GWR.
On a separate note, my understanding that Elizabeth Line trains from Paddington to Reading during 1600-1900 should be off-peak comes form this BRares.com link which does not mention any evening restrictions. The fare was suggested by a very knowledgeable GWR ticket seller at Reading station and until last week it seemed to appear on National Rail journey planners, although they seem to have removed all contactless fares since then.
Separately still, do you know why there are no fares displayed on the Single Fare Finder for Reading to Hounslow West?
Best wishes,
Alexander