As correctly pointed out by petitioner, this sworn statement by respondent is an admission against her interest.

Section 26, Rule 130, Rules of Court (which is of suppletory application) expressly states:

Section 26. Admission of a party. - The act, declaration or omission of a party as to a relevant fact may be given in evidence against him.

The rationale for the rule was explained by the Supreme Court in Manila Electric Company v. Heirs of Spouses Dionisio Deloy:

Being an admission against interest, the documents are the best evidence which affords the greatest certainty of the facts in dispute. The rationale for the rule is based on the presumption that no man would declare anything against himself UNLESS SUCH DECLARATION WAS TRUE. Thus, it is fair to presume that the declaration corresponds to the truth, and it is his fault if it does not.

Respondent's representation in her COC for Senator that she had been a resident of the Philippines for a period of 6 years and 6 months by May 2013 is an admission that is binding on her. After all, she should not have declared it under oath if such declaration was not true.

Respondent's convenient defense that she committed an honest mistake on a difficult question of law, when she stated in her COC for Senator that her period of residence in the Philippines before May 13, 2013 was 6 years and 6 months, is at best self-serving. It cannot overturn the weight given to the admission against interest voluntarily made by respondent.

Assuming arguendo that as now belatedly claimed the same was due to an honest mistake, no evidence has been shown that there was an attempt to rectify the so-called honest mistake. The attempt to correct it in her present COC filed only on October 15, 2015 cannot serve to outweigh the probative weight that has to be accorded to the admission against interest in her 2013 COC for Senator.

Certainly, it is beyond question that her declaration in her 2013 COC for Senator, under oath at that, that she has been a resident of the Philippines since November 2006 still stands in the record of this Commission as an official document, which may be given in evidence against her, and the probative weight and binding effect of which is neither obliterated by the passing of time nor by the belated attempt to correct it in her present COC for President of the Philippines. Respondent cannot now declare an earlier period of residence. Respondent is already stopped from doing so. If allowed to repudiate at this late stage her prior sworn declaration, We will be opening the floodgates for candidates to commit material misrepresentations in their COCs and escape responsibility for the same through the mere expedient of conveniently changing their story in a subsequent COC. Worse, We will be allowing a candidate to run for President when the COC for Senator earlier submitted to the Commission contains a material fact or data barring her from running for the position she now seeks to be elected to. Surely, to rule otherwise would be to tolerate a cavalier attitude to the requirement of putting in the correct data in a COC. In fact, the COC filer, in that same COC, certifies under oath that the data given are indeed "true and correct".