Short answer. Yes. Article 1135 of the Civil Code provides that when an adverse claimant possesses, by mistake, an area greater or less than what the title expresses, prescription is based on the actual possession, not on the area stated in the title. So prescription runs on the smaller area you actually occupy.
What the law says
In case the adverse claimant possesses by mistake an area greater, or less than that expressed in his title, prescription shall be based on the possession
Civil Code, Article 1135 — Possessing More Land Than the Title Shows. Read the full provision →
What Article 1135 says
Article 1135 of the Civil Code speaks to this precisely: "In case the adverse claimant possesses by mistake an area greater, or less than that expressed in his title, prescription shall be based on the possession." The rule looks at what is actually occupied, not at the number printed on the title, and it applies whether the actual area turns out to be bigger or smaller than what the title says.
Why 'by mistake' is part of the rule
The article conditions this on the mismatch arising by mistake — the claimant genuinely believed, in good faith, that the area occupied matched the title. That word is doing real work: the article is not simply saying a title's stated area can be ignored whenever convenient; it is describing a specific situation where an honest discrepancy exists between what the paper says and what was actually possessed, and settling that prescription follows the possession in that scenario. If the mismatch were not a mistake at all — if it reflected a deliberate agreement, for instance, to occupy less than the title covers — the article's own wording about mistake would not squarely describe it, and a different analysis could apply.
Why the rule tracks possession rather than paper
Prescription, as a doctrine, is built around what someone actually does with land over time — occupying it, using it, treating it as their own — not around what a document happens to say. Article 1135 applies that logic evenhandedly: it does not privilege the titleholder's larger claim when possession is smaller, and it does not privilege a claimant's expanded possession when the title says less. Either way, the measure the article chooses is the same one — the area actually possessed.
What this means for your smaller area
Applied to your situation, prescription runs on the area you actually occupy, not on the larger figure your title states. The extra area described in the title but never actually possessed by you does not accumulate any prescriptive period on your behalf simply because the title mentions it. Whatever legal consequence prescription eventually produces — for or against a claim — Article 1135 ties it to the ground actually held, which in your case is the smaller area, not the paper description.