Archivists work to a rule that sounds like superstition and is in fact arithmetic: one copy is no copies. Not because a single copy will certainly be lost, but because a single copy has no margin. Any event that reaches it — a fire, a flood, a house move, a well-meant clear-out, a locked drawer whose key went with its owner — takes the whole record. There is nothing behind it.
Households apply this rule to photographs, which are backed up automatically by the phone that took them, and almost never to the documents that determine what happens when someone dies.
What actually holds only one copy
Start with the will. In England and Wales, a will admitted to probate is generally the original signed document; a photocopy raises questions that cost time and sometimes money to answer. Many households hold exactly one original, in one place, and a meaningful number cannot say with confidence which place.
Then the surrounding material, which is where single-copy exposure is nearly universal. The schedule of what you own. The list of which institutions hold what. The note explaining why the accounts are arranged the way they are. The letter to the family. Insurance schedules. Guarantees. The deed. Property records. None of these has a natural second copy unless someone deliberately made one.
The cruelty of the pattern is that the most useful documents are the least duplicated, because they are the ones nobody else was ever given. Institutional documents — the ones a bank or a registry also holds — can be reconstructed with effort. The household's own explanatory record cannot be reconstructed at all. When it is gone, the reasoning is gone with it.
Two copies means two failure modes, not two objects
The rule is easy to satisfy badly. Two copies in the same house is one copy with extra paper: the same fire reaches both. Two copies on the same laptop is one copy. A document and its cloud sync are frequently one copy in a meaningful sense, because a deletion propagates to both — sync is not backup, and a synced folder faithfully reproduces the mistake you just made.
The requirement is not two objects. It is two independent failure modes. The second copy should be reachable by an event that does not reach the first. Different building. Different custody. Different medium, ideally — because a copy held on paper and a copy held digitally do not fail for the same reasons.
The custody question nobody asks
Making a second copy is the easy half. The half that gets skipped is deciding who is allowed to hold it and who is told it exists.
A second copy that nobody knows about is not a second copy. It is a document that will be discovered during a clear-out, possibly after the estate is settled, occasionally after the house is sold. The point of duplication is availability at the moment of need, and availability requires that someone other than you can name the location without being prompted.
This is where households tend to substitute intention for arrangement. Somebody knows there is a copy somewhere. That is not the same as somebody knowing there is a copy in the second drawer of the filing cabinet at a named address, and being expected to say so.
A copy nobody can name the location of has already failed. It is simply failing quietly.
What good looks like
A household that has applied the rule properly can answer three questions about every document that matters. Where is the first copy. Where is the second. Who, other than me, could produce either one without searching.
Very few households can answer all three for more than a handful of items. That is not a failure of diligence — it is a task nobody ever assigned. But the rule is not demanding, and it is one of the small number of disciplines where the whole benefit arrives the first time you apply it, and never has to be repeated at that intensity again.