I use Schedule 13D and Schedule 13G filings to create a matching between CUSIP identifier and CIK codes used by SEC. Code for the instruction is provided on my github. Every investor who purchase more than 5% of share in the company has to file Schedule 13. In this schedule he discloses information about the purchase together with the information about the company. Among with the other information investors report CUSIP of the purchased company. This disclosure allows to match company information report by SEC with its CRSP records.

For the purpose of my projects, I find this CIK-CUSIP mapping to be more reliable than two similar maps provided by Compustat and WRDS. As CUSIP is not a permanent identifier, I have a different match for each CIK code in every year. First column of the match file corresponds to the year of filings, from which this link was extracted.

This data could be used to match SEC company information (annual reports, prospectuses, beneficial ownership, proxy filings etc.) with CRSP and Compustat.

I am happy to answer the question about this data as well as listen to the potential suggestions.