The document kept through several moves has survived repeated decisions that it still matters.

Every move is a sorting, and anything still in your possession after three of them has been chosen again and again by a version of you who was tired and short of boxes. That repetition is decent evidence. Whatever the paper is, some part of you keeps deciding it is not disposable, even when you cannot say exactly why. Things that survive that many rounds are usually holding something you have not finished with.

Find one item that has come with you through several homes and look at it properly. Either write down why it stays, or let this be the round where it goes.