With the knowledge of the current pandemic situation, perhaps the concept of 'party' and/or 'invite' is a wholly alien concept to the people of the future with access to time-machines. And assuming a similar reaction to current archeology for things they can't explain better than 'artifact was used during religious or reproductive practises' and didn't consider attending.

Exactly. Luckily a solution has long been found. Simply take a log of the stock market back and then pay me a billion dollars to convince me.

(also you could predict variations in the rotation rate of galactic pulsars. That would be pretty convincing for scientists. But who cares about those guys ?)