This is a topic that annoys me with CTRs. Critical vs Non-Critical fields. Yes, we instruct our employees to complete every field we have information for. However, when regulators come in, they might say.... of the 50 CTRs were sampled, 10 were missing occupation. Well.... if we don't have it, we don't enter it..... its a non-critical field. If you want us to ask for it, make it a critical field. Damned if you do, damned if you don't. Businesses send runners constantly that aren't customers of the bank. In a lot of these instances, the CTRs are due to aggregated transactions and information wouldn't have been collected at time of the transaction. So many factors involved.
To the OP's question, all fields are "required" if you have the information, it needs to be entered. I got hung up on comparing critical and required fields for a while myself. Semantics if you ask me. In my opinion, if you want the information, make it a critical field.