Use WRDS to convert any permno or gvkey to a cusip.
A cusip should be 9 digits and can be converted to a Datastream local code by adding a U at the front and dropping the final check digit.
260543103 (cusip) goes to U2654310 (DS local code).
(Datastream local codes can be used to create a Datastream list).
If the cusip is less than 9 digits the leading 0's could be missing, and need to be added.
7525108 (cusip) goes to U00752510 (DS local code).
A 6-digit cusip usually indicates a company and 10 is added to give the primary listing.
Converting via a ticker is also possible but seems to be less reliable.
For a cusip 7525108, in Excel cell A2
=CONCATENATE ("0000" ;A2) - in B2 adds leading zeros
=RIGHT(B2 ;9) - in C2 trims to 9 characters
=CONCATENATE ("U" ;C2) - in D2 adds leading U
=LEFT(D2 ;9) - in E2 drops final checkdigit, giving DS local code.
