The exposed face is not the whole fitting
A premium fitting can have a well-finished visible surface while moisture and salt remain in a thread, washer, joint, fixing point or narrow gap. These areas may dry slowly and receive less effective cleaning than the face of the product.
This is one reason a product label alone cannot predict long-term coastal performance. Base metal, surface finish, fabrication, installation detail, mixed materials and maintenance all matter.
Installation can reduce the risk
The fitting should be installed so water does not remain trapped against the substrate or behind a decorative trim. Fasteners and washers should be compatible with the surrounding material. Stainless screws should not be treated as automatically harmless when they are installed against aluminium or another dissimilar metal.
Sealants should be compatible with the surfaces and used as part of a considered detail, not as a substitute for drainage or access. The actual manufacturer instructions and warranty conditions remain the authority for a specific product.
Read the stainless and aluminium galvanic corrosion guide, 304 versus 316 comparison, and coastal product specification guide before finalising exposed hardware.