Both failure modes are common. Writing access details into a will can expose them to parties who read the probate file. Writing nothing leaves an executor with authority over property they cannot reach.
The mitigation is separation: the legal instrument refers to a technical directive; the directive describes process and locations rather than secrets; and the key material itself sits in a distributed structure with a documented recovery quorum.
This is the layer BlockByte builds, in coordination with the client's solicitor, so that the legal and technical documents point at each other correctly.