Total posts : 45366
Well, in that case, it simply means that it was certified as tested. There are any number of ways the signal can be attenuated for testing and certification, like antenna mismatching. That means staying legal is up to the operator. If, for example, you did anything to boost the signal gain outside of the testing parameters (and we don’t know what they were), it might come to a place where it is in violation in the strictest sense.
But here’s the other side of that coin: The FCC has not issued enforcement orders on anything like your home FM broadcasting unit. They have bigger fish to fry, as in those who buy those 5 watt blasters on eBay. If they catch you with one of those, they will issue a NOUO in relatively short order.
FWIW, and this is a no-fault opinion, I think you’re probably about as safe with your unit as can be expected, what with its Part 15 certification and all. If you get a 1000 ft. to a good receiver, then good for you. In your case, the very worst thing that would happen is they tell you to shut it off … but I think it’s unlikely.