Short answer

Legally existent? Yes—an unnotarized “One and the Same Person” affidavit (OATS affidavit) is a real document you can write and sign.
Evidentiary value? On its own, very limited. It is a private document that does not enjoy the presumption of regularity.
Will offices accept it? Often no. Most government agencies, banks, schools, and employers require notarization before they will act on it.
In court? It can be used only if the affiant (you) takes the witness stand to identify and authenticate it; even then, it’s generally weak evidence if unsupported by records.

What a “One and the Same Person” Affidavit is (and isn’t)

An OATS affidavit is a sworn statement explaining that different names appearing in documents—e.g., “Juan P. Santos” vs. “Juanito Santos,” or “Ma. Teresa Cruz” vs. “Maria Teresa D. Cruz”—refer to one and the same person. It is a common supporting paper used to reconcile minor identity discrepancies across civil registry records, school records, IDs, bank accounts, and employment files.

It does not, by itself, legally correct the entries in a birth certificate, marriage certificate, passport, school transcript, or any official registry. Corrections usually require statutory processes (e.g., petitions under the Clerical Error Law and related rules) or the issuing agency’s formal rectification procedures.

Why notarization matters

1) Nature of the document

Unnotarized: A private writing. It has no built-in presumption of truth. To be given weight in formal proceedings, the signer must be identified in court and the document authenticated.
Notarized: A public document. Once properly acknowledged before a notary public, it becomes self-authenticating—courts and offices generally accept its due execution without needing the affiant to appear (subject to challenges like forgery or duress).

2) Acceptance by offices

Most receiving institutions (PSA/LCRs when processing clerical corrections, DFA for passport issues, SSS/GSIS/PhilHealth/PRC, banks, real estate registries, schools, HMO providers, and many HR departments) routinely require notarized affidavits for identity discrepancies. An unnotarized version is commonly rejected at the counter, even if factually accurate.

3) Risk management

Notarization deters fraud and error by requiring:

Personal appearance (you appear before the notary),
Competent evidence of identity (e.g., government ID),
Notarial formalities (journal entry, notarial seal, and acknowledgment).

When an unnotarized OATS affidavit might still “work”

Informal/private settings: Some private parties (e.g., a small employer updating a payroll record) may accept an unnotarized statement together with strong IDs. This is policy-dependent and not guaranteed.
Court use with testimony: If you testify and identify the document, the court may admit it, but probative value is limited unless corroborated by official records.
Interim submission: A desk officer may temporarily file an unnotarized affidavit to start an internal review, pending notarization. Expect to be asked to replace it with a notarized version.

Common use cases—and what typically happens

Bank KYC/name mismatch
- Likely outcome: Requires notarized OATS affidavit + IDs reflecting both name variants.
Government benefit records (SSS/GSIS/PhilHealth/Pag-IBIG)
- Likely outcome: Notarized OATS affidavit; sometimes extra proofs (birth certificate, marriage cert., school records).
Civil registry discrepancies (birth/marriage/death)
- Likely outcome: OATS affidavit is supporting only. Actual correction follows statutory procedures (e.g., administrative petition for clerical errors or court petition for substantial changes).
Passport or PRC licensing name issues
- Likely outcome: Agency-specific checklists nearly always call for notarized affidavits plus primary civil registry documents.
School or HR records
- Mixed: Some accept an unnotarized statement temporarily, but final action usually needs notarization.

Elements of a strong OATS affidavit (notarized or not)

Include:

Clear title: “Affidavit of One and the Same Person.”
Affiant identity: Full legal name, nationality, civil status, date of birth, address, government ID details.
Statement of discrepancy: Enumerate each variant (e.g., “Juan P. Santos,” “Juanito P. Santos,” “Juan Ponciano Santos”).
Assertion of unity of identity: A categorical statement that all variants refer to you.
Document trail: List the documents where each variant appears (birth certificate, diploma, bank statement, SSS E-1, etc.).
Reason for discrepancy: Common causes—typographical errors, use of nickname/maiden name/abbreviations, clerical omissions, cultural conventions (“Ma.” for “Maria”).
Purpose: Specify the transaction or correction sought (e.g., “for updating my SSS record,” “for bank account consolidation”).
Attachments: Photocopies of IDs and records showing both the correct name and the variant.
Attestation and signature: Signed by the affiant; for notarized versions, include jurat or acknowledgment, notarial seal, and notary’s details.

Notarization basics (practical pointers)

Appear in person before a duly commissioned notary in the same city/province of execution, bringing a valid, unexpired photo ID.
Ensure the notarial acknowledgment/jurat is complete: date and place, notary’s name and commission number, expiry, roll number, PTR, IBP, and seal.
Sign in front of the notary. Don’t pre-sign.
Keep multiple originals; some agencies keep one on file.
If any signatory cannot sign, a notary may require credible witnesses and special wording.
Fees vary by area and complexity; photocopies of IDs are commonly attached and stamped “Certified true copy of the original seen by me.”

Tip: If you used an unnotarized OATS affidavit and it was refused, you can usually re-execute the same text under notarization; you don’t need to rewrite from scratch unless the facts changed.

Limits of what an OATS affidavit can accomplish

It won’t amend civil registry entries by itself. For true corrections or changes (e.g., first name, sex, birth date, middle name), you must use the proper administrative or judicial process, often with PSA/LCR involvement and supporting records.
It doesn’t override primary IDs (passport, UMID, driver’s license). At best, it bridges conflicting records while you pursue the formal fix.
It doesn’t guarantee agency acceptance. Each institution has its own checklist; some require additional proof (baptismal record, school Form 137/138, NBI clearance, barangay/LSC certifications).

Practical strategy if you have name variants

Identify your “anchor” identity: Usually what appears on your PSA birth certificate (or marriage certificate if your present legal name changed by marriage).
Gather corroboration: Primary IDs in the anchor name, plus records that show how/why a variant appeared.
Prepare an OATS affidavit that maps every variant to your anchor identity and attaches critical documents.
Have it notarized. This maximizes acceptance and reduces back-and-forth with counters and evaluators.
Follow the proper correction route for records with permanent effect (civil registry, passport, PRC license). The OATS affidavit is supporting, not curative.

Frequently asked questions

Q: Is an unnotarized OATS affidavit “invalid”? A: Not “invalid,” but weak. It’s a private document with minimal evidentiary value and is commonly unacceptable for formal purposes.

Q: Can a photocopy or scanned copy be used? A: Many agencies want wet-ink originals. Scans may be accepted temporarily, but final action often requires the original notarized document.

Q: Do I need witnesses? A: Not typically. The notary’s acknowledgment and your competent ID suffice. Witnesses may be needed in special cases (e.g., affiant can’t sign).

Q: What if the discrepancy is substantial (e.g., different middle name or birth date)? A: Expect the OATS affidavit to be insufficient by itself. Substantial discrepancies usually require formal correction via administrative or judicial proceedings.

Sample outline you can adapt

AFFIDAVIT OF ONE AND THE SAME PERSON

I, [Full Name], of legal age, [civil status], [citizenship], and residing at [address], after having been duly sworn, state:

1. I am the same person referred to in various documents as:
   a) [Name Variant 1]
   b) [Name Variant 2]
   c) [Name Variant 3]

2. The above discrepancies resulted from [brief reason: typographical error/nickname/abbreviation/clerical oversight].

3. The following records pertain to me and evidence the above:
   – [Document 1: description, date]
   – [Document 2: description, date]
   – [Document 3: description, date]

4. I execute this affidavit to attest that all the foregoing names refer to one and the same person—myself—and for the purpose of [state intended transaction: e.g., updating my SSS records / bank KYC / PSA correction process], and for all legal intents and purposes.

IN WITNESS WHEREOF, I have hereunto set my hand this [date] in [city/province], Philippines.

[Signature over Printed Name]
Affiant
[ID Type, Number, Date/Place Issued]

(JURAT OR ACKNOWLEDGMENT BLOCK FOR NOTARIZATION)

Replace the bracketed parts with your details. If you intend to submit this to an agency or a court, have it notarized.

Bottom line

An unnotarized “One and the Same Person” affidavit is generally not enough for formal transactions in the Philippines. To maximize acceptance and legal effect, execute and submit a notarized affidavit and back it up with official records. Use the affidavit as a bridge, then complete the proper correction process for any document that needs permanent amendment.