All very interesting stuff.
As I have plenty of frames to "play with" from this roll, and as I coincidentally had some Ferricyanide arrive this morning (as I'm going to try some lith printing and wanted to be armed for two-stage), I thought I'd try a bleach and redevelop.
So I've just made a rehalogenating bleach stock of 7.5g/100ml each of Potassium Ferricyanide and Potassium Bromide, diluted some 1+9 and clipped three frames from the dead roll. I bleached this clip in a shallow tray with continuous agitation for about 5 minutes. There remained some image apparent, but mostly gone, including all edge markings. I chose these three frames as they had three sisters originally exposed within a few moments of each other, so I have a before- and after- comparison.
I then gave it a thorough wash.
Then I knocked up some print developer (this is Fotospeed's recommendation for redevelopment after using their Cl10, what the rationale might be I don't know but I thought I'd try it) and redeveloped the clip in that, again with continuous agitation in a shallow tray. Within 3 or 4 minutes there was noticeable redevelopment and a significant increase in density.
They are washing at the moment, and I'll check tomorrow to see how they look.
I wondered whether I'd get much more improvement from a commercial product?