As someone who took many of the reports at Pitreavie I think I can say the value of the information was a bit mixed. Although obviously keeping an eye out for anything of intelligence value, most of the ships were on normal commercial passages. But some took very interesting routes at very interesting times.
In a subsequent appointment where the information was fused with other sources the anomalies became even more apparent. However, while there was a great deal of concern about possible threats both to the UK and the US from carrying people/things into ports at times of crisis, I cannot remember there ever being anything more than int collection being proved.