2) Your film is very old, so there could be enough base fog in there that when you reverse process you get black.
Thanks for your response, but basically I would expect that to lead to less dense negatives after reversal. That is in the original formula of course :-)
3) You are not sure you had the right dilution of RA4 chemicals
Indeed, but the colour developer should act to competition (well, I did not let it complete well, since I was afraid not to have too dense negatives).
I would take your elderly film and use it for B&W negatives, buy modern film and chemistry for colour film and be done with it.
I like the challenge and the process of searching and experimenting is more rewarding than the end result for me. I have enough fresh film, but I would like to make that one work too. Plus its base is too dense for a B&W negative (it seems to have an additional silver anti-haliation layer that only does away in the bleach).