I agree with the potential interpretation that Zorak stated about the agent at secondary thinking that you had not proactively declared something. I'm wondering if we can think of a good way to proactively declare to avoid misunderstandings? For instance, would it be good to say something like, "I am bringing in items in excess of my duty free allowance today. What is the procedure to pay any applicable duty?"

I had a somewhat similar case once at LAX where I was mistakenly sent to the full secondary lane (due to some food items) instead of the intended agricultural x-ray lane. Fortunately, in that case, the agent realized this upon reviewing my receipt showing an agricultural declaration (which we no longer have the benefit of being able to show).