On one day,
we were four. (One day might be today or it might be in the past)
On the next, (After the first day/ second day)
we were three. (A reduced number, a server, something inside a picture, the creators?)
We are not the subject, (Not the goal or topic)
but the format. (How we are arranged, placed, for example a specific date?)
My brain (and spider-senses!) are telling me that it must be related to the past future concept again.