The individual (or a legal guardian) adds themselves to the list so that, if they ever attempt to create an account at a gambling site that uses Integrity for age-verification, the account creation will be denied (or at least Integrity will not give the OK, the site can still ignore the advice).
Should an individual whose name is on the list attempt to open an account with a participating gaming site, Integrity would not return a match (approval) code to the merchant, thus blocking the user’s access to the site.
Unlike a common dynamic from TV & movie, once a gambler has added themself to the SEL, they can just as easily perform deprovisioning (albeit with a 7 day delay).
The identity world spends most of its time worrying about use cases in which attribute flow enables some experience for users, not actively disables.
I'll give you 5 to 1 odds that the Integrity age verification protocol is proprietary. Unnecessarily so.