Short answer. They can be. In a holographic will, where several dispositions are signed but left undated and the last one carries both a signature and a date, that date validates the undated dispositions before it — no matter when they were actually written. So undated entries are not automatically void.
What the law says
When a number of dispositions appearing in a holographic will are signed without being dated, and the last disposition has a signature and a date, such date validates the dispositions preceding it, whatever be the time of prior dispositions.
Civil Code, Article 813 — Several Dispositions on One Occasion. Read the full provision →
How the article rescues undated entries
A holographic will — one entirely handwritten, dated, and signed by the testator — normally depends on its date. Article 813 softens that where several separate dispositions appear in the same will. It provides that when a number of dispositions appearing in a holographic will are signed without being dated, and the last disposition has a signature and a date, such date validates the dispositions preceding it. So a run of signed but undated entries is not lost, provided the final disposition supplies both a signature and a date to cover them.
The date carries backward
The striking feature of the article is the phrase whatever be the time of prior dispositions. The date on the last disposition reaches back and validates the earlier signed entries even if they were in fact written on different, earlier occasions. The law does not require you to have dated each one as you went along. It is enough that the concluding disposition is properly signed and dated, and that the earlier ones are themselves signed. The single closing date does the work of dating the whole sequence of dispositions above it.
Signatures are still required
Read the article carefully: it forgives a missing date on the earlier dispositions, not a missing signature. Each disposition must be signed; only the dating is supplied by the last entry. An unsigned addition is a different problem and is not saved by Article 813. The relief is also confined to genuine dispositions written in the testator's own hand as part of the holographic will. The article assumes a validly executed holographic will to begin with and simply cures the narrow gap of undated but signed entries within it.
Why this matters when the will is probated
Every will must still be proved in probate before it takes effect, and a holographic will invites disputes about authenticity and completeness. Article 813 gives a ready answer to the common challenge that certain entries are void for lacking a date: if the final disposition is signed and dated, those earlier signed entries stand. It does not, however, resolve questions of forgery, of the testator's capacity, or of later alterations made after the dated signature. Those are separate grounds a court weighs apart from the dating rule this article settles.