How an archive decides what to lose
Keeping everything is not an option, and the rules for discarding are stranger than you would guess.
An archive is defined less by what it holds than by what it has agreed to let go. Space, budget and conservation all push in the same direction: most of what arrives cannot be kept.
The criteria are rarely about importance. Condition matters more. So does whether a duplicate exists elsewhere, and whether anyone has requested the item in the last twenty years — a test that quietly punishes whatever was never catalogued well enough to be findable.
Archivists know this and compensate with informal rescues: a box kept on a desk, a folder that never quite gets processed. A surprising amount of what survives does so because somebody liked it.