What I've found when researching (in general) it can get rather complex - thankfully for Terrot a lot is on the web, and of course there would be more public available documents related to legal entities, physical buildings and of course advertisements. The motor-cycle fanboys seem to write the most. Another good source I have found are local researchers doing news articles.
http://terrot.dijon.free.fr/Chronologie.html
End of 1951 - Launch of the scooter - One million bicycles built is reached
May 1958 - the "Etablissements Terrot" come under the control of INDENOR (part of the Peugeot group)
January 1959 - the manufacture of motorcycles is transferred to St Etienne (AUTOMOTO factory)
End of 1961 - Cessation of the manufacture of cycles and motorcycles
1962 - 1970 - the TERROT brand is affixed to cycles and Peugeot mopeds
[ also many Terrot catalogues here:
https://terrot.eu/documentation/catalogue/cycles ]
From here:
https://dijonpassionpatrimoine.fr/usine-terrot-sauvetage-facade/
"Benefiting from a solid reputation, it was not the Second World War and the German occupation of the factory that brought the factory to the ground, but the mismanagement of the shareholders.
In 1953, Peugeot, its historical competitor, took 50% of the capital of Terrot. The brand gradually lost its luster to such an extent that in
1959, the production of motorcycles was relocated to Saint Etienne"
"
Peugeot, not only owner of the factory but of the Terrot brand, used it for a few years before it disappeared in the early 1960s. Peugeot used the Dijon plant for its brand until the 1990s, before selling it to the Japanese company Koyo Steering in 2000."
Reading between the lines a bit (my own words), I would guess already by the mid-50s there was clear trouble. Probably too little market space domestically. Peugeot no doubt consolidated the bicycle manufacture, re-structured it and set it's sights on export too.
).
