I would back up the Keilwerth alto ID and Amati for the soprano sounds about right. I've worked on some of the NYC schools' Concord "Made in Holland" altos and tenors. They don't closely resemble anything else I've seen. One thing that stands out without having one in front of me is the neck receiver slotted in 4 places, every 90 degrees, with a clamp around the top. These horns are 50 year old school horns (one great thing about the NYCBOE/DOE is that, until the '80s, and sometimes after, they engraved the date of purchase into every horn. Some have been around a long time!!), banged up and sloppy, and I've tried to talk the teacher into retiring them but he loves the sound, and I'll keep them going as long as I can. I'd love to run into one in good condition, to see if they were any good before the kids got to them. Very funny that Schenkelaars may have made some horns themselves, but also got stencils from so many sources--and hit-and-miss sources at that.