Hi again, back with an update.....
It turned out that my part A was bad. When I poured the rest of the bad part A into a clear graduate, it was colourless or perhaps slightly yellowish, rather than the pinkish colour of the freshly mixed stuff. I also noticed right away on my first test run with the new solution that, after developing, the developer came out clear and with the same dye colour as the prewet, whereas the bad batch was coming out dirty brown and clearly oxidised. I don't remember what the previous batch was like when new.
Mixing up the new batch brought up some other questions about getting the proper 0.2 g of Phenidone for 100ml of concentrate. How are others handling this? In The Darkroom Cookbook, Steve Anchell suggests making up a solution of 2g Phenidone and 6g Sodium Bisufite in a litre of water. This would require using 100ml to get the 0.2g of Phenidone, which is not very practical for the mixing order in the formula. What if I started with 70ml of this Phenidone solution, add the other ingredients, and then top up to 100ml from the Phenidone solution? Another idea would be to make the Phenidone solution with 10g of Sodium Metabisulfite substituted for the Sodium Bisulphite, so the 100ml would have the right amount both of those ingredients in it. Would this different mixing order cause any problems? Any idea what the life of such a solution would be? It would take me a while to work through a litre, although 500ml would also be a mixable amount. I tried mixing 5g of Sodium Metabisulfite and 1g of Phenidone in 100 ml of water (with the idea of using 20mls in my 100ml concentrate), but the Phenidone was hard to dissolve, and after cooling down it came out of solution again.
Also on the the subject of the Potassium Bromide, how well does a 2% solution of this in water keep? It might be convenient to have a few small bottles of these solutions to mix up, leaving only the Catechol to dissolve from solid.