Understanding Society User Support

I am currently working on the c_ wave but would also like to include some variables from xwave dataset. It seems that there are xwave versions of some variables and c_ versions of the same thing. The c_ version tends to be much smaller with lots of inapplicable cases. However, there seem to be differences between the xwave version and the c_version when you cross-tab them. This is odd and makes me wonder whether the c_ version is a correction of the xwave version (ie they asked respondents things in 2009 and either the information has changed since or the respondent has said, no that’s wrong and so it has been updated).
So coupld you explain to me what is the relationship between the different variables in different datasets, I could hardly find any comprehensive descriptions from the userguid.
Thank you very much!