I've read two articles about the duty-free exemption (1, 2), and in both articles there are three different amounts of duty free item value allowance mentioned: 200 USD, 800 USD, and 1600 USD. However, I can't seem to find any information about how I can figure out which "tier" is applicable to me. The second article does mention looking at a section "on the $200 exemption", but I don't know where I would find this.
How can I know what duty free amount I am allowed to bring into the United States as a citizen returning from abroad?