With the Shimano RS (RS12) the already venerable Skylark design took a couple of small steps forward. The cable clamp was mounted on a Centeron lever, allowing the derailleur to automatically compensate for the need to overshift. Perhaps more significantly the Centeron lever acted on the outer parallelogram plate - changing the geometry of the gear, as previously the cable clamp was attached to the front knuckle.
Despite these changes, the RS is a cheap, basic, tidy, design that is clearly a Shimano Skylark underneath.
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