I do not understand why I sometimes get zeroes for the CPSIDP variable rather than the 14 digit field that hopeful

I am sure that I did something stupid but am unable to figure out what I did wrong. I have successfully downloaded CPS data for 15 variables for April 2013 and April 2014. I was able to match individual respondent in 2013 and 2014 using the CPSIDP variable and checking LINENO, SEX, and RACE for consistency. I found the CPSIDP variable very useful. Here is my question. When I try to do the same thing but with the August 2013 and August 2014 files, I get zeroes for the CPSIDP variable in 2014. The same problem occurs when trying to link the December 2013 and December 2014 files. As I said, I am sure I did something wrong or I simply am not understanding something very basic. Any help would be appreciated.

The zero values for CPSID/CPSIDP in August and December 2014 are a known error in the IPUMS-CPS data. We plan to release corrected data within the next month.

Hope this helps.