The legal principles affecting lost wills are quite simple, but in practice they often raise difficult evidentiary issues. Judges need to infer something as elusive as the intentions of the deceased when a will disappears. The type of weighing of evidence that is involved is quite subjective, and different judges will read it differently. Some of the decisions appear quite surprising, if not perverse. Clients in lost will disputes may be well advised to seek mediation rather than go to trial. Governments should help mitigate the problem by encouraging people to participate in centralized wills registries.
Spiro, Peter S, The Common Law Treatment of Lost Wills (February 1, 2016). Estates, Trusts and Pensions Journal, volume 35, no 2.