Jean-Paul Routens, the present owner of the company was very active as a frame-builder well into the mid- 90s, perhaps even later, and was a very competent builder, working from an "atelier" in the bowels of his shop at Gieres, just outside Grenoble.
The open treatment of the chain and seat-stay ends on this frame are very very typical of French practice, although some of these look pretty rough.
I imported a full range of J-P Routens frames, personally-built ones, from the late 80s into the mid-90s, but even on the cheaper frames eg Columbus Aelle, I dont ever recall seeing a seamed brake bridge. IMO I think that this frame is probably one of the cheaper, possibly demi-course or sports frames, that Routens bought in, although I could be wrong.
As for the appropriateness of this open-end style of stay end..it is certainly more eye- catching than the straight end that often was used by Columbus and Vitus, but it does leave the stay open to the entry of water, salt etc etc etc. It is doubtful if it is needed to vent the joint. A better form of this file-profiled end is to flush in some brazing material with the aim of filling the hole while at the same time retaining the concave flute. By producing an area of brazed material, as opposed just to line contact, this method is far stronger than a void and far more attractive. I have always brazed these joints with silicon bronze..never silver-soldered them..and have often seen them brazed with very strong nickel-bronze . .. and would be interested to hear why other builders have preferred to silver-solder them.
Norris Lockley, Settle Uk