In ActivityPub, "Create" and "Update" are exactly the same. The reason they have different names is the spec writers are jerks. They specify that only the thrice damned go-to-hell-for-coming-up-with-this client-to-server interface can be different between Create and Update, so if you write a sane client that says "fuck you" to those spec writers, then you'll still communicate with other instances just fine, if "Create" and "Update" differ only in name.
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