A date column would be great, because then all I would nee to do is run a pivot table to see what's new or a graph to should a timeline and how well my message is getting through internally.

Agreed! Often I want to know if the password I changed a year ago is pwned, not one from five years ago, like LinkedIn. It's a parallel service, "WhenHaveIBeenPwned?"

I would vote for 2 date columns: one for date of breach, one for date breach was discovered/made public.