Understanding Society User Support

I am looking at data from Wave C, file name c_indresp.sav SPSS file.

I am very interested in targeting households that contain at least 2 siblings. A frequency tabulation of the variables "respondent has a sibling in the household" (c_psiblings) gives:

Proxy = 3,836
yes = 4,496
no = 41,407
Total = 49,739

Inspecting the Data View there are indeed a total of 49,739 cases. So this tabulation seems to be exhaustive, as the sum of the proxy + yes + no responses does = 49,739. My question is, are the 3,836 proxy responses equivalent to a "yes" response?

I can find no relevant advice in the user guide when I search it by variable name or by "proxy", and no relevant advice in the forums. I am confused because if, using the same file, I tabulate the frequencies of the variable "year individual interview started" (c_isyear) I get,

proxy = 3,836
2011 = 26,898
2012 = 17,934
2013 = 1,071
Total = 49,739

Which means the ACTUAL totals of the categories 2011, 2012 and 2013 are uncertain (as it stands) as the given values cannot include the proxy responses, yet, conceivably, some of these 3,836 proxy responses may be from respondents whose interview start year was either 2011, 2012, or 2013 - or some other year.

Any clarification would be very gratefully appreciated.