Workers compensation laws do vary by state and if you perform work in other states then you need to be familiar with the workers compensation state law for that particular state to see if you are required to carry workers compensation.
Any state you currently perform work in at the time of the effective date of your policy must be listed in part 3A of the policy, otherwise you will not have any coverage for that state. It will also provide coverage for those states listed in part 3C of the policy if you were to start operations in those states during the policy period. However, you only have coverage for those states in part 3C up to 30 days after the policy renews and if you continue to operate in those states beyond that time then those states have to be added to part 3A of the policy. Otherwise, you will no longer have coverage for those states.
That 30 day window is a major reason for wanting to have your workers compensation audit completed within 30 days of the policy renewing because if you started work in another state during the policy period then it will be picked up during the audit and should be added to part 3A of the policy as a result of the audit. If you don’t complete you audit in a timely manner and forgot to notify your agent that you started work in another state then you may be left without any coverage in those states.