Short answer. Yes, in substance. An unregistered marriage settlement binds the spouses but cannot prejudice third persons. Registration is required both in the local civil registry where the marriage contract is recorded and in the proper registries of properties before a creditor can be held to it.
What the law says
They shall not prejudice third persons unless they are registered in the local civil registry where the marriage contract is recorded as well as in the proper registries of properties.
Family Code, Article 77 — Form of Marriage Settlements; Effect on Third Persons. Read the full provision →
Valid between you, invisible to everyone else
Registration is not a requirement for validity. A settlement that is in writing, signed and executed before the wedding is fully binding as between the spouses whether or not anyone files it. What registration does is make it effective against strangers to the agreement. The statute says only that an unregistered settlement shall not prejudice third persons, which is a narrower rule than it first sounds: the creditor is entitled to ignore the arrangement, not to have it declared void. Between the couple, and in any accounting between them, it continues to govern.
Two registrations, not one
The provision names two places and both are required. The first is the local civil registry where the marriage contract is recorded, which is a matter of the marriage, not of any particular asset. The second is the proper registries of properties, meaning the registry covering each property whose ownership the settlement affects. A couple who lodged the agreement with the civil registrar and stopped there have done half the job, and the half they omitted is the one a lender examining a land title would actually look at. Where the couple own land in several places, the registry for each is a separate filing.
What a creditor gets to assume
The practical effect is that a bank dealing with one spouse may proceed on the property regime that appears from the public records. If nothing is registered, the creditor may treat the marriage as governed by the default regime and look to the property that regime makes answerable, even though the spouses privately agreed on complete separation. The spouse who is surprised by this is usually the one who assumed a signed and notarised document was self-executing. A notary makes a document authentic; it does not make it public in the sense the statute means.
Check the annotations, then fix what is missing
The question is answered by documents, so gather them: the settlement with its date, the marriage certificate showing the registry where it was recorded, and a current certified copy of the title to each affected property, read for annotations on its face. If the settlement is unregistered, registering it now protects you going forward, but it does not retroactively defeat a creditor who already dealt with you in reliance on the public records. That distinction is what a lawyer will want to sort out first, and it turns on the dates.