All three feel like costs of earning a living, because they are, and all three are generally not deductible. One piece of reasoning explains every one of them.
A dwelling limit set when a policy was written and never revisited is the most ordinary form of under insurance, and the clause enforcing it is easy to miss.
Classification is settled by how a working relationship actually operates, not by what either side agreed to call it. Several different agencies get a vote.
There is no single rulebook for state and local obligations and nobody mails one out. That is why the first notice usually arrives from a state you barely worked in.
Almost nobody reads the letter properly the first time. These are the questions that follow, roughly in the sequence they occur to the person holding it.