I have just managed to unearth a few more snippets of relevant information about Mercier's range of frames.
In September 1975, the firm announced that all it's frame built of Reynolds 531 tubing would have engraved top-eyes, and a Cinelli crown, also engraved.
In September 1977 the firm announced that it was introducing a whole new concept to its top-end-frame - the PRESTIGE range., this being in addition to the COMPETITION range that included the Tour de France, Tour du Monde. Le Contre-la-Montre modles. The article making this announcement did not state whether the PRESTIGE range produced custom models only..but did boast of its 'exceptionelle facture artisanale' ie the range's exceptional craftsmanship., the limiting of the number of frames produced in the range and the fact that each frame would receive its own individual frame-number.
The original Mercier presssed aluminium slightly art-deco headbadge with the frame-number stamped into the lower panel seems to have been replaced in the very early 80s by a very stylised 'M' with a coronet above.
The original Mercier headbadges turn up frequently on French eBay on one of its collectors sites:
http://www.ebay.fr/
Once into that main site enter 'plaques de velo' in the search engine.
Good hunting
Norris Lockley
Settle UK