Thanks, so I guess they're different between C2 and C4 due to different part numbers, but I don't see Carrera S item there?

See below:
http://www.gboxweb.com/997specs.html

 

For the 997.2, until 2011, the self adjusting clutch was limited to the "S", but base also got self adjusting clutch on 2011 models.

 

Some manufacturers use an assembly number and a part number. For instance, in old Ford factory manuals, a C6 and a C4 transmission might be referred to by the same assembly number because they are both transmission assemblies, but they were definitely NOT the same part number.

Also, components could share the same part number but would have different suffixes or prefixes to show engineering changes over time or to indicate slight differences in the part depending on the vehicle or trim level it was installed in. So, two nearly identical items could share the same part number but other identifiers on the two parts could make them non-interchangeable.

I am not familiar with Porsche's numbering convention so having a part number in common does not necessarily prove that the C2 and C2S transmissions are the same unit. I am curious about the answer, though.