You are certainly correct about the number of Subs that have had their Sails removed as part of the storage process. I almost forget sometimes that it is over sixteen years now since I left those Sunny shores.
Anyway, a quick trawl around the internet reveals many relevant images, although most are difficult to date, and it must be remembered that certainly at Devonport, the Boats have to be moved around a bit in 3-Basin as they go into Dry-dock for periodical Hull inspection/re-preservation.
However, i now believe the current situation could be something like this.
Resolutions (x4), defuelled and stored alongside. Sails intact.
Swiftsure, defueled and being dismantled in Dry-dock as the first test of the process. Sail was intact when stored.
Churchill, defuelled and stored alongside. Sail removed.
Dreadnought, defuelled and stored alongside. Sail removed fairly recently?
Valiant, defuelled and stored alongside. Sail removed.
Warspite, defuelled and stored alongside. Sail removed.
Courageous, defuelled and in South-Yard dry-dock as Museum. Sail intact.
Conqueror, defuelled and stored alongside. Sail intact.
Swiftsures (x5), fuel aboard and stored alongside. Sails intact.
Trafalgars (x4 or 5? unsure of Trenchant status), fuel aboard, decommissioning or stored alongside.
Some piccys, second one of which in Devonport is the same as yours from a different angle. I am not sure what structure at the aft end of the one of the hulls you are referring to? Warspite, Conqueror with Sail & Valiant.
Next two are of Dreadnought and Churchill with Sails removed, together with Swiftsure.
Fifth one predates the third and fourth images in that Dreadnought still has her Sail.
Last and first are, I believe, Dreadnought.....now very long in the tooth. Before and after Sail removal.