Remember the good old internet, where niche aficionados could come together and geek out? It still exists! At least, some of the time. I posted my question and the niche aficionados came through. First, with a whole bunch of details about the lugs and other bits and bobs and then with the real breakthrough: it's not from the 1970s! It's almost certainly older, likely post-WW2 French.

[2/n]

https://www.retrobike.co.uk/threads/help-identifying-french-70s.501586/

They key was the derailleur hanger, or, really, the lack there of. The modern parallelogram form for the rear derailleur is not the first design that was tried. So even though this bike has a 70s or 80s era derailleur bolted onto it (a Simplex SO) the fittings on the frame are for a much older style. You can see how it works in the 3rd and 5th photo of this post: https://www.retrobike.co.uk/threads/vintage-french-randonneuers-and-porteurs.449944/page-23#post-3285014

Since this bike has the fittings for that style of derailleur, the frame is almost certainly pre-70s, and probably pre-60s. But, that still doesn't answer who made it, who "updated" it with 70s components, and especially, what of the decals and branding are original and what is from that refurb.

[3/n]

The shiny and generic decals, based on their style, are more likely later additions. But the faint brand painted on the down tube—if I could figure out what it said—might be a clue. Here @no_fuss came up with the breakthrough, pointing me to a list of brands maintained on the wiki of a french vintage bicycle forum. Based on that, the most likely reading of my faint and peeling letters was “R. Teulade”. Unfortunately, neither the wiki nor the french forum had any more information. But then…

[4/n]

But then I found Velos Vintages du Grenier, who on their website have two bicycles branded “R. Teulade” with the exact same cursive script! And what's more, they have the same Champion du Monde decal on the seat tube and a similar decal (but of a different famous race) on the head tube. Except, as noted, the decals appear to be newer than the frame I have. And the two bicycles on their website are quite different from mine. Maybe that means R. Teulade isn't the maker, but the name of someone fixing up old bikes? So I contacted Velos Vintages du Grenier…

[5/6]

https://velosvintagesdugrenier.com/products/velo-vintage-femme-mixte-vert-taille-s-m

And never heard back. Maybe it was the poor quality of my machine translated French? Maybe they just don't have any information or don't know what to say? I don't know. That's the where the trail ends for now. I have started thinking about how to restore this bike, but that will be a thread for another time.

[6/6]