Jenni, at first I thought "three navy coats" sounded excessive too, but then I looked at my own closet and I have a short navy puffer, a long navy puffer, and a long wool coat that happens to be black but could just as easily be navy (bought at a warehouse sale, no other colour options). Three coats is pretty minimal in a climate with a long cold season, and a person who is strict about colour palette may decide that they want a core outerwear capsule in their very best colour, whatever that may be. Otherwise, you may end up reaching for one particular coat in your preferred colour when it doesn't actually suit the weather or level of formality. I could easily see buying a trench, a puffer, and a wool coat all in navy without it feeling like duplication. They'd all serve different purposes, but having a core palette means they can be interchangeable if needed (e.g. they'll all work with the same shoes, bags, accessories, etc.).