Daft question... we know that the Diagrams and CWNs are shown on the SWR website. Are the STPs published anywhere public?
Not a daft question, but suggest that will never happen. STP notices by their very definition are issued very frequently and often very close to the date of operation.
I have no idea who at SWR is responsible for uploading the base plan CWN and unit diagrams for each LTP issue to the publicly accessible website, albeit I was very surprised to see same in the public domain a couple of years ago.
Bottom line is that (in may dinosaur) days and very likely unchanged today, one would issue a STP notice in relation to a given SX week or weekend at the due date in advance of the week or weekend concerned, but then something else would change (outside of Planning's control) and so a further STP notice would be issued within days of the day of operation.
In other words, stations and depots might have several amendments issued to them for any one day within the following week, and it would need someone on each depot or station (or signal box, as I was) to take account of every change issued by HQ (as was) and ensure local notices were updated and distributed in time.
Fire fighting comes to mind, but that's how it was.
If every such notice was added to the SWR web page, I would wager 99.9% of those who look in to the site on a hobby/enthusiast basis, would ignore the same, as it would become too complex to understand in relation to previously issued amendments for the same date.