Short answer. Yes, the list must have existed at the time the will was signed. Under Article 827, a document can only be incorporated into a will by reference if it was already in existence at the moment of execution. A list created after the will was signed cannot be part of the will.
What the law says
The document or paper referred to in the will must be in existence at the time of the execution of the will
Civil Code, Article 827 — Incorporation by Reference. Read the full provision →
Four requirements that must all be met
Article 827 allows a will to incorporate an external document by reference, but only if four requirements are satisfied simultaneously. The document must have existed before the will was signed. The will must clearly describe and identify it, including stating the number of pages. The document must be identifiable with certainty as the one referred to in the will. And it must be signed by the testator and the witnesses on each and every page — with an exception only for voluminous books of account or inventories. All four requirements must be present; failing any one of them means the document is not part of the will.
Why pre-existence is required
The rule that the document must already exist when the will is signed prevents a common form of fraud or manipulation. If documents could be created after the will and then attached to it, the distribution of an estate could easily be altered without any of the formalities that govern wills themselves. Requiring pre-existence means the incorporated document was fixed and definite at the time the testator actually expressed his wishes. A document created after signing could reflect the intentions of someone other than the testator.
What happens if the list was made after the will
If the furniture list your father mentioned was prepared after the will was executed, it does not qualify for incorporation by reference under Article 827 and is not part of the will. The assets it describes would then be treated as assets not specifically disposed of by the will, and they would be distributed according to the residuary clause of the will if one exists — or under the rules of intestate succession if no such clause covers them. The items listed would not go to the persons named in the document.
How to check whether the list qualifies
To determine whether your father's list meets the requirements of Article 827, look first at when it was dated relative to the date the will was signed. Then check whether the will actually describes the list with sufficient specificity — does it mention the number of pages? Does the description match the document you have? Finally, is the list signed on each page by both your father and the witnesses to the will? If any of these elements is missing or unclear, a lawyer can assess whether the document forms a valid part of the will or whether it must be treated as a separate, informal expression of wishes with no legal force.