It is worthy of note that until she was in a nursing home, at a claimed age of 110, "Jeanne Calment" avoided any publicity about her claimed age. For example she refused the local mayor's congratulations when she "turned 100" - instead newspapers wound up running a story about someone turning 95.

She literally waited nearly 50 years after the claimed switch, after she was in a new environment, with new people, without the people who would have most easily challenged it, to publicize her claim. This is exactly what we would expect from someone who was trying to hide a fraud.

Search for "Publicity (lack of)" in https://www.liebertpub.com/doi/10.1089/rej.2018.2167 for more details on that.

But many people who were younger then her remember her during that time period that you say she was only pretending for the taxman. All of these claims are coming from people who live in another country and never did any investigatory field work in the area. Everyone who actually did the interviews and on the ground investigation came to the conclusion that there was no swap, and that the alleged swap wouldn't have made any sense.