Turns out Clymer was jettisoned by its former parent company, the now deceased Penton Media, as non-essential baggage (in Corporate Speak: "to better focus on core concerns and competencies") as its own boat was circling the drain. Clymer was picked up by Haynes at a fire sale price in a bid for broader market share.
I figured it was something like that... why sell just one mediocre maintenance manual for a specific motorcycle model (or range of models), when you can sell two?
Full disclosure - I'm new to the Haynes/Clymer world; when asking for advice from long time owners of a certain model of 40-year-old Honda four, everyone with an opinion has said that the Haynes and Clymer manuals in question are equally disappointing. I ended up with a copy of the Clymer, and after reading it cover-to-cover, I'm inclined to agree. Sketchy details, incorrect (or sometimes multiple) names for the same part, mislabeled diagrams and photos (pretty easily sorted), and outright wrong data, like some clearance and torque specs (not so easily sorted!).
Kind of like the official RE UCE service manual, now that you mention it... must be a long-held tradition in the world of motorcycle maintenance publishing!