Hello, I am an employee of Truro Cathedral and I’d like to clarify that the contested fourth spire does not actually belong to the cathedral proper but is part of an existing structure the cathedral is attached to which is actually its own individual parish church. It’s the only remaining wing of the original St Mary’s Parish Church, and still operates as its own church with the Dean of the Cathedral being the Rector. long story short, the cathedral has three spires and the church has one. Just seen a lot of discourse about this online recently and I thought it might help to have one of us give an explanation. I’m happy to verify my identity. CRBarry (talk)

So there is a very good reason we rely on what reliable sources say instead of contradicting original observation.