I wasn’t trying to derail the thread, I just think accusations that people (and it’s only ever Royal women by the way) “copy” each other as some kind of competitive oneupmanship incredibly silly.
Fashion is cyclical. Anyone who has lived for more than a couple of decades will know this personally. Styles, colours, textures, proportions all make their way into and out of fashion as designers strive for new things. The designers who clothes we buy and whose aesthetic we buy into are influenced by the past, by different cultures, by their own house archives (if you are Dior, etc) by the zeitgeist and by each other, plus a hundred other things. And most of us are just consumers of this output, with no more individual ability to influence it than an individual fish can influence a shoal.
Against that backdrop, no consumer of fashion can “own” a style, a colour, a pattern. They simply see something which a designer has already thought of, designed and had made up. Countless also people will also see and like that same idea.
When it comes to royal women dressing for formal occasions, they are working in a fairly narrow range of choice. They each have favoured designers, but they moment they step out of fully bespoke (like Camilla, for example) there is a high likelihood that someone else will see what they are wearing and think “I like that - I’ll get one too”. So they are not setting the style in any way, just the first to display it in their circle. Sometimes Kate will wear a style first and others will follow her (the teal Jenny Packham evening dress below). Sometimes it will be Mary of Denmark (I think she was the first to wear the ever so popular Beulah day dress). Sometimes Meghan (the Safiyaa caped-style dresses she wore have been worn by any number of Royals, including last week by the Dutch Crown Princess in a beautiful lilac version for the Omani State Dinner).
This doesn’t make any of these women inherently “better” at fashion. It just means they are fishing in the same pool, and have their eyes open - as you might expect.