With all due respect, it seems to me that the documents contradict the claim in the initial email. Rob's initial claim is that Ken came up with UTF-8 entirely

With all due respect, it seems to me that the documents contradict the claim in the initial email. Rob's initial claim is that Ken came up with UTF-8 entirely from scratch, without even looking at IBM's proposal. But Ken's oldest document from Sep 2, 1992 has his changes simply appended after the original FSS-UTF document from IBM (starting at "We define 7 byte types", as mentioned in the email), and notes the changes from original spec. Then the final document that he sent out (Sep 8) is basically the FSS-UTF document with his changes applied (this is also mentioned in the email!). There are two changes, basically: 1. Use 10 instead of 1 as the prefix for continuation bytes, so you can synchronize from an arbitrary location. 2. Once the bits are reassembled, use the value as-is instead of adding a bias constant, which simplifies the code at the cost of a tiny bit of packing efficiency. Given the documentation provided, I would say that the fairest description of the development of UTF-8 is that IBM came up with the initial design, and Plan 9 made two improvements on it to produce the final UTF-8 design.