That was only for a single event. DEFCON no longer requires proof of vaccination or ID.
And as the other commenter said, the information wasn't recorded.
Also, the majority of DEFCON attendees no longer care about being anonymous. It's not this secret underground thing. Many employers pay for their security staff to go to DEFCON. For a few years now, you can even pre-pay for your ticket online with a credit card which makes getting reimbursed for your ticket a fuckton easier. Also means you don't have to carry $500 in cash.
And as the other commenter said, the information wasn't recorded.
Also, the majority of DEFCON attendees no longer care about being anonymous. It's not this secret underground thing. Many employers pay for their security staff to go to DEFCON. For a few years now, you can even pre-pay for your ticket online with a credit card which makes getting reimbursed for your ticket a fuckton easier. Also means you don't have to carry $500 in cash.