I'll see if I can re-find the pic. It's buried in my trove of Yanagisawa sax research.I was most surprised to find out that Yani made flutes at one point. I actually wonder if they were also stencils.
I do think it's possible that the flute could be a stencil, but I doubt it. If Yani always sold stuff through distributors -- Zen-On and Prima Gakki being the big two -- I'd think that buying a stencil, stenciling the Yanagisawa name on it then distributing it through another company is too difficult to be cost effective. However, there are several high-end Japanese flute companies I can think of off the top of my head and maybe one of them thought that having "Yanagisawa" on 'em was better than Sanko or whatever.
On the topic of Keilwerth, etc. making brasswinds, I can easily see the sense in that: my baritone saxophones had more brass in them than most of the trumpet sections I've worked with. However, being able to work with brass doesn't necessarily make you into a great trumpet maker .