Common required states are written in the file common1.cns that is stored in the Mugen system files. In the DEF file of the characters, you have to specify the filename containing your common states. Usually, you will find stcommon = common1.cns which means that be default, Mugen tries load the file from the character directory first then in the Mugen data file if not found.
With c-wind, the character has its own common1.cns file that is correctly referenced in the DEF file. The problem was that its common1.cns contains overriden (redefined) states not all the required states! To counter that I renamed its common1.cns to common10.cns than I added the common10.cns as a state file in the def. It does the trick since Mugen is going to load common1.cns in its data files then override the common states by reading c-wind common10.cns.
If you overwrite the files, c-wind will have her own common1.cns and a common10.cns files with the same contents, which means that the required common states will be missing again because common1.cns will be back.
Was it clear enough?