CUSIP is a 9 character long identifier. The last digit is a check sum checking the first 8 previous characters. This seems to me that it is not possible for two securities to have the same 8 characters and different check sum. I know this is not exactly quantitative, but I haven't found a forum where I could ask.

Source: https://www.cusip.com/cusip/index.htm

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    $\begingroup$ No, for exactly the reasons you state, two CUSIPs cannot differ in inly the last digit. The last digit is a function of the first 8 digits, and any ordered set of 8 digits has only one proper checksum. If two CUSIPs are the same except for rhe last digit, one of them is not a CUSIP, and in fact making that determination is the very purpose of the checksum digit $\endgroup$
    – Dan Bron
    Nov 21, 2014 at 12:16

1 Answer 1


No, 9th character is computed using deterministic algorithm described here: http://en.wikipedia.org/wiki/CUSIP#Check_digit_pseudocode.


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