Part of it would depend on whether or not it has, as required of all self propelled ships above a low threshold GRT, an AIS transceiver. If it’s got one, and it’s on, I can find the ship in seconds (access to multiple large terrestrial and satellite AIS systems at work).
But I guess if they never intend to go anywhere near Port State Control, they could just turn their AIS off. People do it all the time to violate sanctions, avoid pirates, etc.
BroBot9000