I am going through linking march monthly to asec using cpsidp. However, I see some 0 cpsidp in march monthly sample. Is this possible or am I missing something?
CPSIDP values of 0 should only occur in the ASEC oversample, and not for individuals who are in the March Basic sample. You should double check which sample these are occurring in. If you have an extract with both March Basic and ASEC samples, you can check which rows correspond to which sample using the variable ASECFLAG. More info on CPSIDP can be found on its description page.