Updated
Service books go missing with remarkable ease: left in the glovebox of the previous car, packed into a box during a house move, or ruined in the garage. The good news is that the book is not the vehicle's history. It is only a copy of it, and a history can be rebuilt.
Many people try to get the dealer to reissue the original book. It is almost never possible, and more to the point it achieves nothing: a new empty book proves nothing. What has value is not the book, it is the stamps and the invoices that were inside it.
In order of how likely they are to work:
Collecting the paper is not enough: it has to be readable by a stranger. For every job you recover you need four facts, always the same ones: date, mileage, what was done, who did it. If the mileage is missing, check the invoice: nearly every garage writes it down.
Photograph each document as you find it, even in a hurry. Paper gets lost a second time just as easily as the first.
The paper book has a flaw that no amount of care can fix: it is a single physical object, and single physical objects get lost. The same is true of the folder of invoices, the envelope in the drawer, and the folder on a computer that is in no backup.
The alternative is to record each job at the moment it happens, somewhere that does not depend on a physical object and that you can show a buyer without having to search for anything.
Garage Saga does exactly that: you photograph the invoice, the fields fill themselves in, and the photo stays attached as proof. It is free, and when you sell, the history passes to the new owner instead of starting again from nothing.
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