Maybe post June 1978 when Renault Alpines won Le Mans. All the ELF Alpines retired in ignominy with engine failure in 1977 (at about the same time and for the same reason as the year before), I doubt Renault would have been celebrating that.
Thanks Howard, that makes good sense. I remember thinking at the time that it would have been nice if they had actually driven the car around the circuit under its own power - and I found the photos:

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