CGS identifiers ensure that essential front- and back-office functions run smoothly, enabling custodians and sub-custodians to easily communicate, manage and examine the details of a transaction for accurate and efficient clearance and settlement. Derived from the Committee on Uniform Security Identification Procedures, CUSIPs are 9-character identifiers that capture an issue’s important differentiating characteristics for issuers and their financial instruments in the U.S. and Canada.
Lets "Key" in on important differentiating characteristics for a moment.
The original WAMU shares were required to have a unique CUSIP. An easy search in history shows the CUSIP: 939322103
This was before the bankruptcy existed, and for some time.
Move forward and the stock is no longer trading, Litigation Trusts is created to pay off creditors. However, in court the subject is brought up about what if there is enough money in the waterfall to reach the lower classes holding shares? 19-22 How can we differentiate previous owners that signed releases and MAY (not will), but may, have assets left over to distribute.
Easy, there is a method for that. A CUSIP can be generated to reflect a unique identifier. In this case, the LT had a new CUSIP issued and replaced digits 4-6 (322) with ESC (Escrow).
The LT said they didn't think they were needed and that the waterfall would not likely reach these classes but agreed to issue them anyway. Which also gave them the power to remove them. Which they did.