Never claimed to be a know it all. I just posted what your State put out. It says the 2015 IPC is adopted and uses the word Mandatory in their official documents. Why would they have a mandatory plumbing code and then disregard it in favor of a general, all encompassing code? Doesn’t quite make sense. I’m sure you will come up with some innocuous reason.
Retirement is nice. I am actually busier with projects now since there is no excuse to ignore them any longer. New shop and barn going in, new arena going in. Just finished a little over 600 feet of new fencing. Outdoor agility arena prepped for new fencing and gates. Then when the rains come, I fly to my Santa Barbara home where it is being updated. The updates are tough being a block off the beach with the warm weather.
The thought is that the IRC is sufficiently comprehensive for residential construction. You don’t need specialty inspectors for each system (electrical, mechanical, plumbing, building). One inspector certified to the IRC can do it all. Personnel costs has a lot to do with it.
PS. I’m not retired. Just went back to home inspections full time when the recession ended.