mau,
pipedia is a truly great resource. scott thile is to be honored for his immense achievement, as are all the individuals who have contributed content. the website remains a work in progress, though, and riddled with incomplete or inaccurate statements. these generally get identified and corrected by many contributors as time goes by. it should go without saying that it will never be "complete" or 100% accurate.
the marechal ruchon question you raise about the persistence of the company's name is a case in point.
in the first place i'm not sure that marechal was ever a "brand' in the sense that we generally mean when talking about pipes (if i was home now i could consult my library and perhaps address this question). marechal was a company that owned and manufactured pipes under the gbd brand. i'm not sure that it ever made pipes under the marechal marque. in any case if what is meant is the survival in any form of references to marechal, then here's a quick experiment you could try: if you have the patience for a little firsthand digging, go to worthpoint.com and do a search for gbd hallmarked pipes. you'll come up with over 200 relevant listings (i.e. gbd hallmarked pipes offered for sale over the last dozen years or so; some of the listings will of course be duplicates). many of the hits won't have adequate descriptions or photos to settle the question, but a number will. this is how i was able to say that AO appears on gbd silver bands through at least the beginning of the 1920s but apparently not thereafter. you can do a similar analysis addressing the marechal issue. i think you'll find that even a cursory examination shows that mr&c continued to be stamped on gbd silver bands at least until the 1950s. only a paucity of data enables us to set a proper end date.
i'll also note in passing that the pipedia reference to cadogan is misleading, and founded on faulty information. cadogan was formed in stages, the first and most important taking place on july 24 1928. on that date the main parties reached and executed a deal: the adler family contributed oppenheimer pipes, marechal ruchon, h. perkins, and their u.s. and canadian entities; the salmon family contributed civic, loewe, and la bruyere; the deguingands kicked in their uk and french businesses. later that year reiss premiere joined in, and early in 1929 the comoy/chapuis families came aboard. in return for contributing the equity of their various businesses, the families each received equity (mostly preferred, with a tranche of ordinary a shares and a sprinkling of ordinary b shares) in the new holding company. not all animals in the barnyard are equal; in this case the salmon and adler families were the 800 pound gorillas and remained that way for decades, until john adler bought the salmons out in (as i recall) the sixties.
the point is that marechal ruchon (in the form of mr&c hallmarks) continued to be used for decades after the cadogan merger.
best rgds,
jon
