My experience on the Ribble Link is the same. Preston Docks Harbourmaster monitors CH 14. The nearest Coastguard station is Holyhead on Anglesey which has relay masts at Liverpool Bay and on the Fylde Coast, however, Savick Brook is in the shadow of both of them.
Tarleton Lock on the River Douglas (L & L Rufford Branch) is supposed to monitor CH 74 around high tide but I've never heard a squeak on CH 74 in the area.
To be legal, the answer is 'yes'. I would go ahead and do the course anyway. You'll learn a lot more than how to press the PTT button !