The pairing of damping rate with spring rate might not be perfect as Subaru intended but it will work. Similar to if you were to put aftermarket lowering springs on your stock shocks - who knows what
exact damping rates those springs were designed for.
As @
gpvecchi beautifully summarized in this post, the Sachs dampers change every few years - possibly from minor changes in damping rates to continuously improve the car. But there's no data to support this so we can only assume.
The Sachs dampers on the tS claimed to be "tuned by STi" but they're
not even branded STi anywhere on them.
Until someone compares a yellow Sachs with a purple Sachs back to back on the same spring and car for example, we won't know how great the difference in damping rates are.