How do I keep up with tricky local building codes?

You have reached the point where the everyday code is second nature. What still catches you are the complex, jurisdiction-specific corners, the rules that change from one town to the next. That is not a sign you are behind. It is the nature of a field where the ground keeps shifting under you. Nobody carries all of it in their head, and the ones who seem to do not either. What they have is a system: they know which authority to call, which reference to check, and they check it rather than guessing. Mastery here is less about memory and more about knowing where the answers live. Start building your own map. For the jurisdictions you work in most, keep a simple file of contacts and the sections that bit you before. Next time an unusual requirement surfaces, add it. Over time you are not memorizing the code; you are building the reference you can trust.