Here's an outline of the case made by proponents of the "identity switch" hypothesis — put forward mainly by Russian gerontologist Valery Novoselov, laboratory technician Nikolay Zak, and later physicist Philip Gibbs — along with its current standing, since mainstream longevity scientists overwhelmingly reject it.

The hypothesis

The claim is that Jeanne Calment died of tuberculosis in 1934 at age 59, and that her daughter Yvonne (born 1898) then assumed her identity, mainly to avoid inheritance taxes on the family estate; the woman who died in 1997, officially aged 122, would in fact have been Yvonne at 99 ( CBS News,  Straits Times).

The evidence proponents cite

Motive

• Avoiding French inheritance tax after the deaths of Jeanne's father (1931) and allegedly of Jeanne herself in 1934, plus a possible pre-1934 annuity contract that would keep paying out only if "Jeanne" survived ( Europe PMC).

Documentary and signature evidence

• Financial documents from 1931–1933 show a clear, sudden, and permanent change in Jeanne Calment's signature — before the recorded 1934 death — which proponents say can only be explained by a different person signing ( Zak & Gibbs).
• A 1930s identity card: it's unclear why Jeanne needed one at all (she had a passport), and Yvonne's own signature differs sharply from Jeanne's earlier stable autograph ( Zak & Gibbs).

Physical mismatches

• The identity card lists dark eyes, a low forehead, and a height of 1.52 m — details proponents say jar with her later appearance (lighter eyes, measured height around 1.50 m in old age, which they attribute to Yvonne being shorter) ( CBS News).

The 1931 tuberculosis episode

• A 1931 photo places "Yvonne" on the terrace of the Belvedere sanatorium in Leysin, Switzerland — but proponents argue the patient was actually Jeanne. Testimony from Luc-Régis Gilbert, son of the sanatorium's director Dr. Maurice Gilbert, holds that his father was surprised by Calment's later fame "because he had treated her at the Belvedere" ( Calment Validation).
• No confirmatory hospital records of Yvonne's treatment in Arles were found, and Mme Calment herself was vague ("we took her to... Oh! I don't recall any more") ( Europe PMC).

Testimony slips and "mistaken identities"

• In interviews she described being escorted to school by a maid, Marthe Fousson — records show that could only be true for Yvonne, not Jeanne ( Zak & Gibbs book).
• Multiple inconsistencies in her famous Van Gogh anecdote and in other recollections, which proponents read as Yvonne's borrowed memories ( Zak & Gibbs book).
• Analysis of the 15 hours of INSERM interview recordings released in 2022 claims to reveal numerous identity slips ignored by the original validators ( Zak & Gibbs book).
• Other circumstantial items: the closed casket and heavy veil at the 1934 funeral; Yvonne's name absent from the family tombstone; Calment reportedly ordering old photos burnt once she became famous ( Europe PMC,  CBS News).

Validation and plausibility arguments

• Calment never satisfied the classic validation criterion of public recognition of her 100th birthday (no local press coverage in 1975) ( Europe PMC).
• Novoselov argued her muscle tone, ability to sit unaided, and absence of dementia were medically anomalous for a 120-year-old ( CBS News).
• Zak and Gibbs later published a Bayesian analysis and a "switch scenario" paper arguing the balance of evidence favours the switch, and called for DNA testing of the remains ( SocArXiv,  Bayesian assessment).

Status of the hypothesis

The claim is rejected by the original validators (Jean-Marie Robine and Michel Allard) and by the broader scientific community. A 2019 Franco-Swiss study in the Journal of Gerontology re-examined the case and concluded the switch claims rest on inaccurate or unrelated facts; it noted a 1934 local press report that a "particularly large crowd" attended Yvonne's funeral — hard to square with a deception unless dozens of Arles residents were complicit in a prominent, well-known family ( Oxford Academic,  SWI swissinfo). The same study's modelling found that while rare (roughly one in ten million), reaching 122 is not statistically impossible ( SWI swissinfo), and French researchers called the Russian work amateur science that met none of the standards of scientific publication ( France Inter,  Inserm). No exhumation or DNA test has been authorised by the French authorities, so the question remains formally unresolved in the eyes of proponents while the record stands as validated.