Mike Radio has been heard above 6200 several times in the last 3 months.
Now an evidence that this is out of a licence, but even last year Mike Radio seemed to behave quite strangely for a licenced station.
Of course, we don't know the terms of the Dutch licences for the SW stations. Apparently, the quieter stations seemed to get a main frequency and an alternate frequency, a better idea for SW than a fixed frequency. Frequencies outside of the broadcasting bands can be used for broadcasting on the basis of not disturbating the established users, that can explain 3920 for example. But 1 kW carrier power is hardly low power on a maritime frequency.