This blog on my companion site www.WillCaveat.com discusses a handwritten will (holographic will) and whether the beneficiaries of that handwritten will can testify as to what the testator (maker of the will) said concerning the date of the document. The Deadman Statute governs this kind of evidence
The Holographic Will (this means a handwritten will in the testator’s hand)
Issue: Was the Holographic Will written before or after a typed Last Will and Testament drafted by an attorney?
How the Deadman Statute restricts evidence of what the testator said on my willcaveat.com site: Deadman Statute and Breaking a Will Legal