went

 went  is a way to express, in plain text, an RSVP *yes* value, when posting an RSVP to an event that was attended in the past, that is, posting of the RSVP after the fact. IndieWeb Examples: http://tantek.com/2016/336/t3/went-trails-motion-film-festival.

Silo's
On Meetup.com, the RSVP yes is shown as 'going' for future events and 'went' for past events. It is not possible to add your RSVP after the event.