NEVER try to mix common sense and the EPA, it just plain does not work because their decision making process does not include any common sense.
As far as I know,,no slow to medium speed engines of any kind are EPA approved. As for what they advertise the less honorable of the Chinese will take anyone's money for non-approved engines and set them on a ship because once there they have done their duty. Getting them off a ship at port is the buyers problem.
I have two cute little 9 HP Chinese diesels in the shop that are at least EPA tier 3 legal but they are small displacement 2 cylinder high speed engines. The EPA regs are too complicated for anyone outside of "the loop" to understand. An example is the air cooled Yanmars and China clones of same. The 10HP engines are legal, the little 3.5s are not ? I have not seen any of the mid sized 6HP or L70s lately? maybe the have been banned too?