"If you have work on the effective date of this policy in any state not listed in 3A, then coverage will not be provided for that state unless the insurance company is notified within thirty days."
That is the standard wording found in most WC policies across the country. But it is easy to fail to understand the importance of identifying all states of operation upfront and including them all in 3A.
Let's say a Texas-based employer has a job in Louisiana at the policy's effective date; there is no coverage for work in Louisiana unless you notify the carrier within 30 days. It does not matter if that job is just two days in Louisiana or whether another job is the one that has the claim; the coverage for Louisiana is non-existent, EVEN IF Louisiana is listed in 3C.
The worst part is that it is usually free or minimal cost to add a state to 3A.
Gulf Coast States:
Especially marine businesses move across the four Gulf states, many of them almost daily. We strongly recommend adding all four Gulf states, Texas, Louisiana, Mississippi & Alabama to 3A for any business operating in the Gulf.
If you have a marine business, in say, San Diego, you may well never leave California, but if you are in Rhode Island, then you probably work in four states pretty much daily.
Ensure ALL states where the insured COULD work are listed in 3A, just in case of ongoing work at the effective date.