So I worked with Ilford tech support who told me that the DD-X is not too old and my film should be fine too so they said that the main film I'm having trouble with, Delta 3200 is touchy and I'd just need to make adjustments. I'd been using the same sort of adjustments I'd had to make for HC when I first used that combo which was a mistake as the times, while appearing similar in the table gave very different results for me in practice.
This morning I did a triple clip test souping a leader from a roll shot at 3200 for 9:30, 12:00 and 17:00, the recommended times (IIRC, working from memory here) for 3200, 6400 and 12800 EI which seemed like good starting points. Actually, I'm fibbing a bit: since my darkroom was cold and I didn't want to try and maintain a temperature bath through clip tests and final development I used it at 18.5C which, from tables on Ilford fact sheets meant I was actually doing the clip tests for 12, 17 and 20 minutes.
I'd developed a roll before for 13 minutes since a minute past the 6400 mark usually worked for me with HC and it came out thin so I was not surprised when the 12 minute clip came out too thin. The 17 minute clip was better but still not great but the 20 minute clip looked good!
So, going for broke I loaded my Delta 3200 roll, poured the developer in the tank and agitated for the first 10s of every long minute of a 20 minute development. Then Ilfostop. Then Ilford Rapid Fixer for 5:00. Then the 5, 10, 20 inversion wash cycle with Ilfotol wetting agent in the final wash.
The results were still drying this morning when I left for work so I couldn't make any prints (or, cough, hybridphoto.com methods) to check but from looking at the still drying negs held up to the tube lighting the results look good. The shadows look excellent going down (in the negative) still to 'white' for the blacks I was expecting and the highlights go to black. I will need to see if the highlights have blocked while getting the density I wanted, the leader can still be seen through but it isn't thin like it was at 13:00 in 19-20C before.
Hopefully the prints will look good as I like what DD-X does for the grain of this film, just didn't love the D-max. If I can solve both simultaneously, i.e. if this longer time hasn't accentuated the grain then I will be a very happy camper.
It still sounds to me like a long time to reach d-max but perhaps DD-X gets less active in a cooler darkroom than HC. I'm rarely at 20C unless I use a bath and then I'll usually at 22-23C so I do wonder if HC needs less additional time for cold temps though I follow the adjustment graphs from both sheets so I thought I'd made the correct adjustments. Test, test, test I guess.