I could be off base, but based on what you’ve described, I would recommend finding a fitter that has a saddle pressure mapping pad. Real-time saddle pressure mapping would allow you to pedal and see the changes in pressure as your weight shifts. I would bet a lot of money that the highest pressure areas that show up on a pressure map match up with the areas that you have the recurring issues.
What you described, firm subcutaneous ‘nodules’, are due to pressure, not due to hair, abrasion, or lack of cleanliness. Those would manifest differently. The subcutaneous ones are deep, firm, painful, and my experience also took 5-10 days to disappear. You also mention that its worse on the road bike and on TT bike when spending more time in the horns, those positions would put more pressure through the seat. I suspect when you’re in a TT position you are likely rotated more forward and the weight is on different areas of your seat and more on your arms which reduces the peak pressure on the seat interface.
I had the hard, subcutaneous ‘sores’ like you describe for years and had implemented a number of mitigation strategies (thicker padding, lowering saddle, etc.) Last fall I went to a bike fitter and the fit included saddle pressure mapping and it was eye opening due to previously unidentified asymmetries in my pelvis. All of my reoccurring problem areas lined up with the highest pressure areas from the pressure map. Exactly. Seeing the pressure map in real-time and comparing it to what I was feeling and my history of issues was like opening my eyes for the first time. Everything clicked and the picture started to come together.
What ended up (mostly) solving the problems was rotating the saddle back (not what I expected) just the right amount and switching to a leather / plastic version of the saddle from the full carbon version. This allowed me to actually move the saddle up and back and get better leg extension while cutting peak pressure significantly. Due to my narrow bone structure switching to a snub nosed saddle or wider saddle would have made the problem worse. I had also cycled through a number of different saddles over the years and had temporary relief, but they didn’t address the real issue: peak pressure.
I think the key is figuring out the sit bone width, so you can test an appropriately narrow or wide saddle, figuring out the tilt on the saddle, and then dialing in leg extension and setback to minimize the peak pressure. We used the pressure map many times throughout the first 2 sessions to make sure the changes were not spiking peak pressure.